sat_chen
take the integration of (sin5x)*(sin3x)dx



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amoodarya
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first
sin5x sin 3x =1/2{cos(5x+3x)  cos (5x3x)}

sat_chen
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how in the gods name did you get that

amoodarya
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dw:1359154820627:dw

sat_chen
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the only trick we know so far are the trigonometric identities and half angle formula

sat_chen
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so confused ...

amoodarya
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understand ?
i use product to sum formula

sat_chen
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oh okay thanks

amoodarya
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sat_chen
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ive never seen that format of sum for sine before thanks. is there other ways to do it or is that it

amoodarya
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other way is to expand sin 5x ,sin 3x
but its harder
i send there formula 4 you

sat_chen
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i guess ill have to remember the sum rule then :P

sat_chen
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the other one you sent is not gonna be much help in the long run probably. thanks a lot though

amoodarya
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and 3st way
write sin5x=sin4x+x
and sin 3x=sin4xx
so you have conjugate union if expand them
it is easier than 2nd way (that i said)