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- May 16th 2007, 11:16 AM #1

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- May 16th 2007, 11:20 AM #2

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- May 16th 2007, 11:37 AM #3

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Hello, iceman!

Knowing that: .cos(a + x) .= .cos(a)·cos(x) - sin(a)·sin(x)

show by derivation that: .sin(a + x) .= .sin(a)·cos(x) + cos(a)·sin(x)*a*is a constant.

If "by derivation" means "differentiation", the proof goes like this . . .

Differentiate the given equation:

. . . . . . . . . . .-sin(a + x) .= .cos(a)·[-sin(x)] - sin(a)·cos(x)

. . . . . . . . . . .-sin(a + x) .= .-sin(a)·cos(x) - cos(a)·sin(x)

Multiply by -1: .sin(a + x) .= .sin(a)·cos(x) + cos(a)·sin(x)