Verify (1+sin(y))(1-sin(y))=cos^2(y):

Working from the left side we show that it is equivalent to the right side:

(1+sin(y))(1-sin(y))

=1-sin^2(y)

=cos^2(y) using the pythagorean identity

Verify (1+sin(y))(1-sin(y))=cos^2(y):

Working from the left side we show that it is equivalent to the right side:

(1+sin(y))(1-sin(y))

=1-sin^2(y)

=cos^2(y) using the pythagorean identity