Question 904342
Suppose there is an angle theta where pi/2 <= theta <= pi. Also, sin theta = a. Find cos theta in terms of a.
use x for theta
reference angle x is in quadrant II where sin>0, cos<0
sin(x)=a
cos^2(x)+sin^2(x)=1
cos(x)=-&#8730;(1-sin^2(x))=-&#8730;(1-a^2)