SOLUTION: 1-2cosL+cos2L= ? L is alpha and please if anyone can explain it to me i would be grateful.

You can put this solution on YOUR website!
1-2cosL+cos2L= ?
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1-2cos(alpha)+cos(2alpha) = ?
1-2cos(a) + cos^2(a)-sin^2(a)
1-2cos(a) + cos^2(a)-(1-cos^2(a))
1-2cos(a) + 2cos^2(a)-1
2cos^2a-2cos(a)
[2cos(a)](cos(a)-1)
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Cheers,
Stan H.