SOLUTION: Prove that (sin3A + sinA)sinA + (cosA - cosA)cosA = 0

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Question 1136234: Prove that
(sin3A + sinA)sinA + (cosA - cosA)cosA = 0
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

(sin3A + sinA)sinA + (cosA - cosA)cosA = 0->need correction-> (cosA - cosA)cosA should be (cos3A - cosA)cosA


%28sin%283+A%29+%2B+sinA%29sin%28A%29+%2B+%28cos%283+A%29+-+cosA%29cos%28A%29+=+0+
sin%283+A%29%2AsinA++%2B+sin%5E2%28A%29%2B+cos%283+A%29%2Acos%28A%29-cos%5E2%28A%29=0
....since %28sin%5E2%28A%29-cos%5E2%28A%29%29=-cos%282+A%29 we have



%282sin%5E2%28A%29+-1%2B2cos%5E2%28A%29%29+cos%282+A%29-cos%282+A%29=0
%282%28sin%5E2%28A%29+%2Bcos%5E2%28A%29%29-1%29+cos%282+A%29-cos%282+A%29=0
%282%2A1-1%29+cos%282+A%29-cos%282+A%29=0
cos%282+A%29-cos%282+A%29=0
0=0