# trig

posted by
**Paul C**
.

Show that 1-cos2A/Cos^2*A = tan^2*A

1-cos2A/Cos^2*A =

[Cos^2(A) - Cos(2A)]/Cos^2(A).

Substitute:

Cos(2A) = 2Cos^2(A) - 1:

[1 - Cos^2(A)]/Cos^2(A)=

Sin^2(A)/Cos^2(A) = tan^2(A)