(3-4sin^2a)(1-3tan^2a)=(3-tan^2a)(4cos^2a-3)

Answer 1

3-4sin^2a = (3sec^2a-4tan^2a)*cos^2a = (3(tan^2a+1)-4tan^2a)*cos^2a = (3-tan^2a)*cos^2a
1-3tan^2a = 1-3(sec^2a-1) = 4-3sec^2a = (4cos^2a-3)/cos^2a

now just multiply and the cos^2a factors cancel