[1-sin^2(alfa+beta)]/cos^2(alfa+beta)

Answer 1

[1-sin^2(alfa+beta)]/cos^2(alfa+beta)
= cos^2(alfa+beta) / cos^2(alfa+beta)
= 1

(remember .... 1 - sin^2 x = cos^2 x)

Answer 2

remember that 1=sin^2 Theta + cos^2 Theta, so

1-sin^2 Theta=cos^2 theta