Question

A point in polar coordinates is given, Find the corresponding rectangular coordinates for the point.

(r,Q) = (4, 3pi/2)

I know that you are suppose to use
x=r cos Q and y=sin Q but I do not know how to plug this in.

Answer 1

3 pi/2 is straight down the y axis
x = 4 cos (3pi/2)
but cos 3pi/2 is 0
so x = 0

sin 3pi/2 = -1
so y = -4
so (0,-4)

Answer 2

if (r,Q) = (4, 3pi/2)
then r = 4 and Q = 3π/3

now just substitute ...
x = 4cos 3π/2 and y = 4sin 3π/2
x = 0 and y = 4(-1) = -4
so the point is (0,-4)