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Mathematics 4 Online
OpenStudy (anonymous):

Can someone help explain how to do this integral and get the answer?

OpenStudy (anonymous):

\[\int\limits_{}^{}\cot^5xsin^2xdx\]

OpenStudy (amistre64):

general idea is to change everything in terms of sin cos parts; then cancel what can be canceled

OpenStudy (anonymous):

how would i do that?

OpenStudy (amistre64):

waht another way to write cot?

OpenStudy (anonymous):

yes

OpenStudy (amistre64):

\[cot\ne yes\]

OpenStudy (anonymous):

??

OpenStudy (amistre64):

write cot in terms of its sin cos parts .....

OpenStudy (anonymous):

Lol

OpenStudy (anonymous):

you are mean

OpenStudy (anonymous):

bye. no medals for you!

OpenStudy (amistre64):

we dont do this for the medals, we do it to help people study the material. can you rewrite cot in its sin cos parts?

OpenStudy (anonymous):

no. i don't know what you mean!

OpenStudy (amistre64):

there are two basic trig functions, sin and cos these function can be used to define every other trig function, and they are taught to a student before they take calculus 1

OpenStudy (anonymous):

i know that. i have no idea what to do with that

OpenStudy (amistre64):

by redefining the cot in its sin cos parts, we can simplify the integrand to something more workable

OpenStudy (amistre64):

\[cot^p~nsin^q=\frac{cos^p~sin^q}{sin^p}=cos^p~sin^{q-p}\] this is hopefully a simpler integrand since cos and sin are derivatives of each other

OpenStudy (amistre64):

got a spurious "n" in that ....

OpenStudy (anonymous):

ok but what do i separate? can you like give me the first step

OpenStudy (amistre64):

that was the first step \[cot=\frac{cos}{sin}\] using this in the integral will simplify it to:\[\int cos^5(x)~sin^{2-5}(x)dx\] \[\int cos^5(x)~sin^{-3}(x)dx\] still thinking about how to go from there tho

OpenStudy (amistre64):

the wolf does not give a pretty result ......

OpenStudy (amistre64):

looks like it would have to go thru some "by parts"

OpenStudy (amistre64):

this is getting messy .... hmmm, try a usub maybe? u = sin^2x du = 2 sinx cosx dx du/2sinx cosx = dx \[\frac12\int \frac{cos^5}{sin^5~sin~cos}\] \[\frac12\int \frac{cos^4}{sin^6}du\] \[\frac12\int cot^4u~csc^6u du\] this at least gets us to derivative parts ....

OpenStudy (amistre64):

and from there its still a bunch of "by parts" calculating ....

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