Question

Suppose sin(B)=.75. Calculate cos(A)

Answer 1

We use the formula (sinB)^2 + (cosB)^2 = 1;
But, sinB = 3/4;
Then, (cosB)^2 = 1 - 9/16;
(cosB)^2 = 7/16;
cosB = + or - √7 / 4;

Answer 2

SinB = 0.75

Recall:  Sin²B + Cos²B = 1

0.75² + Cos²B = 1

0.5625 + Cos²B = 1

Cos²B = 1 - 0.5625
 
Cos²B = 0.4375

CosB = + or -√0.4375

Cos B ≈ + or -0.6614