integration

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mdbdidjdksnd
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#1
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#1
How do I get cos2t-cos4t from sintsin3t?
It's part of an integration question and the mark scheme doesnt show the steps for this part.
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mqb2766
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(Original post by mdbdidjdksnd)
How do I get cos2t-cos4t from sintsin3t?
It's part of an integration question and the mark scheme doesnt show the steps for this part.
Use the product to sum formula
https://en.wikipedia.org/wiki/List_o...uct_identities
then integrate
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mdbdidjdksnd
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#3
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(Original post by mqb2766)
Use the product to sum formula
https://en.wikipedia.org/wiki/List_o...uct_identities
then integrate
Okay, thank you. But where is this formula from? Is it supposed to be given to us in the a level maths exam cause I never learnt this.
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mqb2766
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(Original post by mdbdidjdksnd)
Okay, thank you. But where is this formula from? Is it supposed to be given to us in the a level maths exam cause I never learnt this.
Cant say for definite what you have/should have covered. But it is a 1 line derivation from the usual angle sum / difference identities so
cos(2t) = cos(3t-t) = cos(3t)cos(t) + sin(3t)sin(t)
cos(4t) = cos(3t+t) = cos(3t)cos(t) - sin(3t)sin(t)
then subtract.
Last edited by mqb2766; 4 weeks ago
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_Rusty_
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#5
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(Original post by mdbdidjdksnd)
How do I get cos2t-cos4t from sintsin3t?
It's part of an integration question and the mark scheme doesnt show the steps for this part.
Learn double angle identities
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mdbdidjdksnd
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#6
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#6
(Original post by mqb2766)
Cant say for definite what you have/should have covered. But it is a 1 line derivation from the usual angle sum / difference identities so
cos(2t) = cos(3t-t) = cos(3t)cos(t) + sin(3t)sin(t)
cos(4t) = cos(3t+t) = cos(3t)cos(t) - sin(3t)sin(t)
then subtract.
okay, thank you!
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