numerical integration - How to numerically integrate this integral

I am unable to do this definite integral in Mathematica 9.
Is there any command so that I can get the numerical value of the above integration?

Code:

A1 = (A*2^2*Sin[theta]*Cos[theta])/((1 - (2^2*Cos[theta]^2)^2))
A3 = NIntegrate[A1, {theta, 0, (Pi/2)}]