Help in Calculating a Value - Trigonometry

Hi, I had this sum for an exam and I couldn't get it, so I just wanted to know how to solve it:

Given: sinA + sin^2A = 1

Calculate: cos^12A + 3cos^10A + 3cos^8A cos^6A 2cos^4A 2cos^2A - 2

I didn't know how to use the code, so I used ^ for power. Sorry for that.

This is what I did:

sinA + sin^2A = 1

sinA = 1 - sin^2A

But, 1 - sin^2A = cos^2A

Therefore, sinA = cos^2A

...And then I substituted cos^2A as sinA throughout this:

cos^12A + 3cos^10A + 3cos^8A cos^6A 2cos^4A 2cos^2A - 2

Yet, I could not arrive at an answer. All help is greatly appreciated.

Thanks,

RoH.