iOS SDK CGAffineTransform Angle Question

I need to get angle in radians. I have:

CGFloat angle = asin(myImage.transform.b);

This seems to be not working. I need to extract the angl开发者_开发问答e of 'myImage' at any moment in time. How would I extract this?

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CGFloat angle = atan2(card.transform.b, card.transform.a);

That does it.