Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Finding exact values for trig functions of acute angles.

I have $\sin \theta = 3/5$.

I know that $y = 3$ and $r = 5$.

How the heck do I get $x$ if I don't know the angle?

share|improve this question
1  
Again, please put some tag in addition to "homework". –  Arturo Magidin Jun 6 '11 at 1:34
    
I don't know how, it won't allow me to create new tags. –  Adam Jun 6 '11 at 1:34
1  
what exactly are x,y,r and $\theta$? –  gfes Jun 6 '11 at 1:35
1  
@Adam: You don't have to create tags; you just have to use the ones that already exist, like [trigonometry]. List apropriate tags, separated by spaces. –  Arturo Magidin Jun 6 '11 at 1:35
1  
What are $y$, $r$, and $x$? And how is it you "know" $y$ and $r$? –  Arturo Magidin Jun 6 '11 at 1:37

2 Answers 2

up vote 1 down vote accepted

If you know that $y=3$ and $r=5$, then because (presumably) the triangle is a right triangle with legs of length $x$ and $y$, and hypotenuse $r$, by the Pythagorean theorem we have that $$x^2+y^2=r^2,$$ hence $$x^2+9=25.$$ Thus $x^2=16$, and therefore $x=4$.

share|improve this answer

You can draw a picture, too. That makes keeping things straight easy.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.