Use the addition formulae to find an expression for cos²(A+B)+sin²(A+B). Verify that your expression reduces to 1.
Use a similar method to find an expression for cos²(A+B)-sin²(A+B). Verify that this reduces to cos(2A + 2B)
So I get the the stage: cos²A(cos²B + sin²B) + sin²A(-sin²B + cos²B) = cos²A + sin²A(-sin²B + cos²B).
What can I do with the 'sin²A(-sin²B + cos²B)'? I can make it 'sin²A(2cos²B - 1)', but how would that help?
Please help
Use a similar method to find an expression for cos²(A+B)-sin²(A+B). Verify that this reduces to cos(2A + 2B)
So I get the the stage: cos²A(cos²B + sin²B) + sin²A(-sin²B + cos²B) = cos²A + sin²A(-sin²B + cos²B).
What can I do with the 'sin²A(-sin²B + cos²B)'? I can make it 'sin²A(2cos²B - 1)', but how would that help?
Please help