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- October 11th 2010, 10:33 AM #1

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## sin(u)cos(v) != cos(v)sin(u)??

I need help understanding these trig identities:

Where I see this identity I also see it followed up by this identity:

Huh? I recall that:

So cos(b)sin(a) becomes:

Right? but this is NOT equal to the sin(a)cos(b) equation above. Shouldn't it be?

I know that xy=yx so shouldn't cos(b)sin(a) = sin(a)cos(b)?

Where is my logic flawed...

- October 11th 2010, 10:39 AM #2

- October 11th 2010, 10:58 AM #3

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- October 11th 2010, 11:01 AM #4