We can simplify the expression cos^2a + tan^2a cos^2a as follows:
cos^2a + tan^2a cos^2a = cos^2a(1 + tan^2a)
Using the identity 1 + tan^2a = sec^2a, we get:
cos^2a(1 + tan^2a) = cos^2a sec^2a
Using the identity sec^2a = 1/cos^2a, we get:
cos^2a sec^2a = 1
So the simplified expression is just 1.