Please help! If cos(A) = x find cos(2A)?

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Please help! If cos(A) = x find cos(2A)?

How do you do this problem? I usually don't like asking for homework help here, but I just have no idea how to approach this problem since I never learned how to do it.

2007-09-03 14:01:53 · 3 answers · asked by KM 2 in Science & Mathematics ➔ Mathematics

3 answers

Recall the cosine double angle formula:

cos(2A) = 2 cos^2 A - 1
Since cos A = x, you have 2x^2 - 1.

2007-09-03 14:09:55 · answer #1 · answered by Derek C 3 · 1⤊ 0⤋

The double angle formula for cos is
cos(2a) = 2 cos(a) ^ 2 - 1
= 2 x^2 -1

2007-09-03 14:11:39 · answer #2 · answered by norman 7 · 1⤊ 0⤋

cos(2A) = 2x

2007-09-03 14:07:07 · answer #3 · answered by the dude 1 · 0⤊ 3⤋