Simplification explanation 1- (3/8) ^ 2

Dec 2019
10
0
Windsor Ontario Canada
1) \(\displaystyle \sin^2 (\theta) + (3/8) ^ 2 = 1\)
2) \(\displaystyle \sin^2 (\theta) = 1 - (3/8) ^ 2 \)
3) \(\displaystyle \sin^2 (\theta) = 55/64 \)


I'm a bit lost on how the simplification of step 2 to 3 occurs. Typing into my calculator, I get the correct 55/64, but I'm not sure how to do it by hand.