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)
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)