- #1

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i just need to know how to start this, i cant use u-du...

i cant borrow anything....

so how would i start this?

- Thread starter CellCoree
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- #1

- 42

- 0

i just need to know how to start this, i cant use u-du...

i cant borrow anything....

so how would i start this?

- #2

Tide

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Is the integrand the same as

[tex]\frac {\cos {6x} - \cos {20x}}{2}[/tex]

?

[tex]\frac {\cos {6x} - \cos {20x}}{2}[/tex]

?

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- #4

Hurkyl

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Another approach, if you've learned the necessities, is to replace the sine function with its definition in terms of complex exponentials.

Another way is to use the angle sum identities. Your problem is that 7x and 13x have different coefficients, so break 13x into 7x + 6x and use the sum of angles identity for sine. Rinse, and repeat until you can do all of the resulting integrals. One thing you should

- #5

ehild

Homework Helper

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YES!!Tide said:Is the integrand the same as

[tex]\frac {\cos {6x} - \cos {20x}}{2}[/tex]

?

You know, [tex]cos(\alpha +\beta )= cos(\alpha )cos(\beta ) - sin(\alpha )sin(\beta) \mbox { and } cos(\alpha -\beta )= cos(\alpha )cos(\beta ) + sin(\alpha )sin(\beta)\mbox. \\ [/tex]

[tex]\alpha = 13x \mbox{ and } \beta = 7x [/tex]....

ehild

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