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November 14th, 2017, 04:21 AM   #1
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Question Trigonometrical Equation, don't know how to simplify it

Hi everyone.

I have an expression
-cos(f)*(sin(g)*cos(m)*cos(l) + sin(g)*sin(m)*sin(l)) + cos(g)*sin(f)

which is equal to
cos(g)*sin(f) - cos(f)*sin(g)*cos(l - m)

according to Wolfram Alpha's CAS.

I have no clue how to get there.

Thanks in advance,

Peter

Last edited by skipjack; November 14th, 2017 at 05:09 AM.
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November 14th, 2017, 05:08 AM   #2
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-cos(f)*(sin(g)*cos(m)*cos(l) + sin(g)*sin(m)*sin(l))
= -sin(g)cos(f)(cos(m)cos(l) + sin(m)sin(l))
= -sin(g)cos(f)cos(l - m)

Now add cos(g)sin(f) to both sides.
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November 16th, 2017, 03:08 AM   #3
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Thank you so much skipjack
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