Question 851076
Is an acute angle and sin 0 is given. Use the Pythagorean identity 
sin^2 + cos^2=1 find cos 0 
(a) sin 0= (6/7)
(6/7)^2 + cos^2(t) = 1
cos^2(t) = 1-(36/49)
cos^2(t) = 13/49 
cos(t) = +/- sqrt(13)/7
===============================

(b)sin 0= (sqrt(21))/5
(21/5)^2 + cos^2(t) = 1
cos^2(t) = 1 - 21/25 = 4/25
---
cos(t) = +/- 2/5
--------------------------
Cheers,
Stan H.
========================