1,230 reputation
317
bio website andrew-christianson.github.io
location Los Angeles, CA
age 23
visits member for 3 years, 3 months
seen Dec 14 at 21:03

Sep
22
comment calculus of variations question
@Rut welcome to math.se! Posts of this nature should usually be comments on the main question rather than answers. The latter are generally reserved for complete solutions to the problem at hand.
Sep
22
comment Sum of Infinite Surds
I'm not quite sure I understand precisely the value you're computing. Is it: $$\sqrt{10+\sqrt{100+\sqrt{1000+\cdots}}}$$
Sep
21
revised Is the square root of -1 rational?
added 35 characters in body
Sep
21
comment Trig to determine distance: boat on course parallel to shore.
Draw it out first. Can you see how the boat's path in the problem forms a triangle?
Sep
21
answered Is the square root of -1 rational?
Sep
21
accepted Intuition for the Product of Vector and Matrices: $x^TAx $
Sep
18
answered Cubic equation - finding coefficients
Sep
18
comment Cubic equation - finding coefficients
I agree with the above comments that this is not at all the appropriate form for this question. That said, if I interpret your variable names correctly, you fit the parabola with equation $$ax^2+bx+c$$ through three points, $p_1=(x_1,y_1), p_2=(x_2,y_2), p_3=(x_3,y_3)$ and propose to do so with the equations $$ a=\frac{((y_2-y_1)(x_1-x_3))+((y_3-y_1)(x_2-x_2))}{(x_1-x_3)(x_2^2-x_1^2)+(x_2-x‌​_1)(x_3^2-x_1^2)}$$ $$ b= \frac{(y_2-y_1)-a(x_2^2-x_1^2)}{x_2-x_1} $$ $$c = y_1-ax_1^2 - bx_1 $$ and are asking for a similar equation to fit a cubic through three (or four?) points.
Sep
18
comment Intuition for the Product of Vector and Matrices: $x^TAx $
@Alex I know what matrix multiplication means, I'm asking for ways to perform it quickly, or at least 'know' categorical/broad stroke information about the products at a glance.
Sep
17
asked Intuition for the Product of Vector and Matrices: $x^TAx $
Sep
17
revised Is it possible to practice mental math too often?
edited tags
Sep
17
comment Is it possible to practice mental math too often?
George, what sort of arithmetic are you practicing? Is your question more about getting basic times tables down, or how to do more complicated 2+ digit multiplication/mulitiplication by fractions?
Sep
8
revised How do these cross products work
Added vector hats
Sep
8
comment How do these cross products work
I know links aren't always the most helpful, but I would refer you to: en.wikipedia.org/wiki/Cross_product#Algebraic_properties I often find it helpful to have the list of properties as reference when learning how to deal with a new operation (like the cross product).
Sep
8
suggested approved edit on How do these cross products work
Sep
7
awarded  Yearling
Jun
19
revised $E[x\mid x>1]$ if $X \sim \exp(\lambda)$
Convert to Latex
Jun
19
suggested approved edit on $E[x\mid x>1]$ if $X \sim \exp(\lambda)$
Jun
19
answered Difference between supremum and maximum
Jun
19
answered Perimeter of Triangle in a Right triangle.