Trigonometric functions (both geometric and circular), relationships between lengths and angles in triangles, and other topics relating to measuring triangles.

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4 views

compute $E[\sin(\omega_0t+\Phi)\sin(\omega_0t+\omega_0\tau+\Phi)]$

assuming that $\Phi$ is uniformly distributed over $(0,2\pi)$ compute: $$E[\sin(\omega_0t+\Phi)\sin(\omega_0t+\omega_0\tau+\Phi)]$$ I have solved the problem as continues: $$\begin{align} ...
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0answers
22 views

Trigonometry - Application of Sine and Cos rules

Postman Pete leaves the post office and makes deliveries for 2.5 km on Aiden Rd, which is on a bearing of 072 degrees True from his starting point. Pete then heads due north of Sari Boulevard for a ...
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2answers
25 views

Triangle $ABC$ is isosceles with $AB=AC$, and $D$ is the midpoint of $AB$. If $\angle{BCD}=\angle{BAC}=θ$, then $\cos θ$ equals…?

Triangle $ABC$ is isosceles with $AB=AC$, and $D$ is the midpoint of $AB$. If $\angle{BCD}=\angle{BAC}=θ$, then $\cos θ$ equals...? I was doing some UKMT past paper questions - this question is ...
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1answer
28 views

Looking for an alternative proof of the angle difference expansion

I have thought about this for a while and have no progress. Does there exist a purely Euclidean Geometric proof of the Angle Difference expansion for Sine and Cosine, for Obtuse angles?
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1answer
85 views

When $\cos(\theta) = 1/8$ it's easy to show $\theta$ is an irrational angle. Is it algebraic?

Along the lines of my lines of my previous question about irrational angles "$45^\circ$ Rubik's Cube: proving $\arccos ( \frac{\sqrt{2}}{2} - \frac{1}{4} )$ is an irrational angle?", I was working on ...
3
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1answer
60 views

How to find unkown height of triangle without hyptenuse

I been trying to solve this question and have tried to solve it for many days, but do not know how, any help would be much oblidged. A cable company owns the roads marked with the dotted lines in ...
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2answers
44 views

Solve the equation $(tan θ − 2)(9 sin^2 θ − 1) = 0$

Solve the given equation. (Enter your answers as a comma-separated list. Let $k$ be any integer. Round terms to three decimal places where appropriate. If there is no solution, enter NO SOLUTION.) ...
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3answers
24 views

Write the trigonometric expression as an algebraic expression

Write the trigonometric expression as an algebraic expression. $6 \cos(2 \cos^{-1} x)$ Can someone explain to me how to do this? I tried it on my own after watching a youtube video from patrickjmt ...
3
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1answer
58 views

When is the cosine of $\pi/n$ of a certain form?

I have a few questions concerning $\cos(\frac{\pi}{n})$. Are there characterizations for the values $n \in \mathbb{N}$, such that $\cos(\frac{\pi}{n})$ ... is an algebraic number? ... can be written ...
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0answers
39 views

How to solve equation like this [on hold]

A trigonometric equation has the following solution: $ x=20°+n*15°$ where n is an integer . which answer(s) of the of the following answers give(s) the exact same result, note that m is also an ...
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2answers
25 views

Show that any 2D vectors can be expressed in the form…

(a) Show that any 2D vector can be expressed in the form $s \begin{pmatrix} 3 \\ -1 \end{pmatrix} + t \begin{pmatrix} 2 \\ 7 \end{pmatrix},$ where $s$ and $t$ are real numbers. (b) Let $u$ and $v$ be ...
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5answers
54 views

Trigonometry identity $\csc x\cot x=\frac{\cos ^3x}{\sin^2 x}+\cos x$

How to prove that $\csc x\cot x=\frac{\cos ^3x}{\sin^2 x}+\cos x$? I tried manupulating the left hand side but ended up in $\frac{\cos x}{\sin^2 x}$. Can someone show me? Thanks in advance.
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2answers
49 views

Trigonometry problem

Okay..this one simple problem but I am really stuck and have no idea how to start.. $\cos(a-b)+\cos(b-c)+\cos(c-a)=-\frac32$ we need to prove $\cos(a)+\cos(b)+\cos(c)=\sin(a)+\sin(b)+\sin(c)=0 $
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3answers
34 views

If $a \sin \alpha = b \sin \beta$, then show that $ b \cot\alpha + a \cot \beta = (a+b)\cot \frac{\alpha +\beta}{2}$

The question is: If $a \sin \alpha = b \sin \beta$, then show that $$ b \cot\alpha + a \cot \beta = (a+b)\cot \frac{\alpha+\beta}{2} $$ Could I get any hints to the problem? When do I need to ...
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4answers
31 views

prove that $\sin^2 b +\sin^2 c - \sin^2 a= -2\cos a \sin b\sin c$. [on hold]

I tried nearly but couldn't prove it afterwards. Please tell me the the way to prove this. The conditions of the problem is that $a+b+c=0$.
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0answers
30 views

solve another system of three equations [on hold]

I have: $x=\dfrac{-.5b-.5c+.25d}{b+c+d}$ $y=\dfrac{.5b\sqrt{3}+.5c\sqrt{3}+.25d\sqrt{3}}{b+c+d}$ $z=b+c+2d$ I need help moving the $b$, $c$, and $d$ to the Left-hand-side; and moving the x, y, and ...
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2answers
50 views

Finding the Zeroes of a Second Derivative to Determine Points of Inflection

I have been told to graph the function $y=\cos \left(x^2\right)$ for $-2π ≤ x ≤ 2π$. I have determined key features of the graph but need help when it comes to determining the points of inflection for ...
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2answers
36 views

Trigonometric Form of Complex Numbers question. [on hold]

What is the following quotient expressed in polar form: $$\frac{10(\cos(35^{\circ})+ isin(35^{\circ}))}{5(\cos(100^{\circ}) +i\sin(100^{\circ}))}?$$ Please enter your answer in cis notation and ...
3
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2answers
85 views

How to prove an identity (Trigonometry Angles--Pi/13)

In this page http://mathworld.wolfram.com/TrigonometryAnglesPi13.html I found equation (11) and (12). $$\cos^2\frac{\pi}{13}+\cos^2\frac{3\pi}{13}+\cos^2\frac{4\pi}{13}=\frac{11+\sqrt{13}}{8}$$ ...
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0answers
21 views

Smoothly interpolating between functions to create a bouncing wave

How can I create a function which allows me to control the roundness of a wave so I can transition between an Round Wave -> Linear Wave -> Inverted Round wave? I've made a function which creates a ...
2
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3answers
80 views

Find max of $S = x\sin^2\angle A + y\sin^2\angle B + z\sin^2\angle C$

Let $x$, $y$, $z$ are positive constants. $A$, $B$, $C$ are three angles of the triangle. Find max of $$S = x\sin^2\angle A + y\sin^2\angle B + z\sin^2\angle C$$
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2answers
61 views

Solve $2+ \cos{\frac{3x}{2}} + \sqrt{3} \sin{\frac{3x}{2}} = 4\sin^2{\frac{x}{4}}$

$$2+ \cos{\frac{3x}{2}} + \sqrt{3} \sin{\frac{3x}{2}} = 4\sin^2{\frac{x}{4}}$$ My try: $$ \cos{\frac{3x}{2}} + \sqrt{3} \sin{\frac{3x}{2}} = \sqrt{4}\left(\frac{\sqrt{3}}{2} \sin{\frac{3x}{2}} + ...
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2answers
14 views

In the sin of two angles are equal, then proving that two angles are equal - w.r.t different traingles

From the text book: What do they mean by: Therefore, AC/PR = AB/PQ ? Is the / division or ratio? What rule says that AC/PR = AB/PQ in this example? What do ...
4
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2answers
66 views

$D, E, F$ are respectively projection of $O$ on $BC, CA, AB$. Prove that $\cot{\angle ADB} + \cot{\angle BEC} + \cot{\angle CFA} =0$

Let $O$ be an arbitrary point located inside the triangle $ABC$. Let $D, E, F$ be (respectively) the projections of $O$ on $BC, CA, AB$. Prove that $$\cot{\angle ADB} + \cot{\angle BEC} + ...
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0answers
26 views

why $\cos 2x$ is positive for $0 < k < 1$? [on hold]

The reflex angle x is such that $\sin x = –k$, where $0 < k < 1$ How to explain why $\cos 2x$ is positive for $0 < k < 1$?
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1answer
31 views

find the exact value of $\cos^2x$ and $\csc x$. [on hold]

Given that $x=\tan ^{-1}(\frac{1}{3})$, find the exact value of $\cos^2x$ and $\csc x$. How to find this without using calculator?
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2answers
56 views

Find the smallest value of $x$ such that $10\cos\left (\frac{x+1}{2}\right)=3$ [on hold]

Given that $x$ is measured in radians and $x > 10$, find the smallest value of $x$ such that $$10\cos \left(\frac{x+1}{2}\right)=3$$ How to solve this question? I've no idea.
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1answer
36 views

Show that $x^2+y^2$ is constant for all values of $\theta$.

Given that $x=3\sin \theta-2 \cos \theta$ and $y=3\cos \theta+2 \sin \theta$ i)Find the value of the acute angle $\theta$ for which $x=y$ ii)Show that $x^2+y^2$ is constant for all values of ...
4
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0answers
33 views

Generalized Trigonometric Functions in terms of exponentials and roots of unity

I am trying to come up with generalized trigonometric functions using the exponential definition that we use today for the trig functions sine and cosine $$\sin x=\frac{e^{ix}-e^{-ix}}{2i}; \cos x ...
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1answer
27 views

Express various trig functions in terms of the sine.

The acute angle $x$ radians is such that $\sin x = k$, where $k$ is a positive constant. Express, in terms of $k$. i) $\sin (2\pi-x)$ ii) $\tan(\frac{1}{2}\pi-x)$ iii) $\cos (\pi+x)$ My attempt: ...
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1answer
33 views

Show that the angle between $OP$ and the normal to the curve at $P$ satisfies the following

I'm struggling to answer the following question below I've already worked out the gradient to the curve at $P$, but I'm having difficulty answering the second part of the question. MY attempt is as ...
3
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2answers
59 views

Easy question Find $\sin 2x$, $\cos 2x$, and $\tan 2x$

Ok so I was absent from school yesterday because long story short I had no way to get to class b/c something happened last minute. I'm pretty sure this is easy but I keep getting the wrong answer for ...
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3answers
34 views

Value of Sine Function from data given [on hold]

If $0 \le \alpha , \beta \ge 90\ $ and $ \tan(\alpha - \beta) = 2$ and $\tan (\alpha + \beta) = 3 $, Then what is the value of $\sin 2\beta$ ?
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4answers
87 views

Find the area of a triangle given the radius of its incircle and a tangential point

A friend gave me recently the following interesting problem and I would like to share a couple of solutions. Any additional contributions are welcome. A triangle $\vartriangle ABC$ is given and we ...
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1answer
53 views

Maximize the trigonometric expression

Find the maximum value of $$4\sin^2 x+3\cos^2 x+\sin(x/2)+\cos(x/2)$$ Please give some hints. I tried writing the angles in half-angles but it didn't help. Thanks.
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2answers
50 views

How to calculate an elementary integral

How do you calculate $$\int\dfrac{2 du}{(u^2+1)^2}$$ It does not seem too difficult but I do not know which method to use.
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1answer
32 views

Help with primitive function

I need help evaluating the indefinite integral $$\int\frac{\cos(5x) + \cos(4x)}{1-2\cos(3x)}dx.$$
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1answer
65 views

Calculation of integral using two different methods? [on hold]

Find $$\int \dfrac{x^3}{(x^2+1)^3}dx$$ in two different ways, first using the substitution $u=x^2+1$ and then using the substitution $x=\tan \theta$. I managed to do both of these but the answer is ...
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0answers
12 views

Find Intersection of Two Circle given Lat/Lon and radius

I am attempting to calculate the intersection of two circle on the Earth with a given latitude, longitude and radius. I started with this post. While I am using this in the context of programming, it ...
2
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7answers
43 views

Some help on trigonometric equation

So I have $\sin^3x = \frac 34 \sin x$. Can you expand so the answer is either $\sin x(\sin^2x +\frac 34)$ which leads to the answer $\frac 12 + 2n\pi$ or that $\sin^3x = \frac 14(3\sin x-\sin^3x) - ...
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3answers
44 views

Find the number of integral values of $k$ if $ \sin4x - \cos4x + 3 \sin2x= k$

Please help me with this question How to find the number of integral values of $k$ that satisfy the given equation: $$ \sin4x - \cos4x + 3 \sin2x= k$$ My attempt: On solving the above equation, the ...
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1answer
24 views

Evaluating sin using sum/diff identities

EDIT: IM DONE WITH THIS PROBLEM, THANKS FOR THE HELP Evaluate the expression under the given conditions. My work (got lost and don't know what to do from here): EDIT: Sin theta should be -3/5 ...
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1answer
29 views

Sum/Difference Identity Formula Question

Wouldn't this be, per the sum/difference identity formula, $\cos (\frac{13\pi}{5}-\frac{\pi} {5})$ which is $\cos (\frac{12\pi}{5})$?
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0answers
52 views

Zeta function, how to solve a finite geomatry summation.

I wanted to solve the zeta function for an undifend period "$d$". So for every $d\ge2$. $$\zeta(-s)= \frac{1}{(d^{s+1}-1)}\sum_{m=1}^{\infty} \frac{1}{2^{m+1}}\sum^{m}_{j=1} ...
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1answer
38 views

'Chasing sides' in a geometry problem

Consider the circle $W=x^2+y^2=81$. Let $AB$ be a diameter of circle $W$. $AB$ is extended through $A$ to $C$. Point $T$ lies on $W$ so that line $CT$ is tangent to $W$. Point $P$ is the foot of the ...
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2answers
54 views

Trying to solve a pair of trigonometric simultaneous equations

I have a machine that has two shafts which are the inputs and their position is set by 2 servo motors. Depending on the angle of these two shafts (shaft 1 has an angle designated $Ta$ degrees, shaft 2 ...
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votes
2answers
51 views

How to find sin and cos of 0, pi/2, pi without calculator [on hold]

In my notes it shows how to calculate by using the unit circle. But I do not know why the value of sin is the y coordinate and the value of cos is the x coordinate.
2
votes
0answers
58 views

proving a inverse trigonometric expression

Show that $2 \tan^{-1}\frac{\sqrt{x^2+a^2}-x+b}{\sqrt{a^2-b^2}}+\tan^{-1}\frac{x\sqrt{a^2-b^2}}{b\sqrt{x^2+a^2}+a^2}+\tan^{-1}\frac{\sqrt{a^2-b^2}}{b}=n\pi$ I tried algebric simplification,but was ...
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0answers
26 views

Rotating one coordinate system about another

I have two coordinate systems: A and B. I also have a point p, whose position relative to ...
1
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2answers
57 views

Prove that type question of Trigonometric Identities

If $3\sin A + 5\cos A = 5$, then prove that: $$5\sin A + 3\cos A = ±3.$$