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I have checked and rechecked my problem the whole way through and I can't figure out what is wrong with it, I would really really like to know what I did wrong.

 

0π/3(cosx)(sin3x)dx

 

Next I just rearranged things:

 

10π/3(cosx)1/2(sin2x)(sinx)dx

 

which equals:

 

10π/3(cosx)1/2(1cos2x)(sinx)dx

 

then I defined variables to use for substitution:

 

u = cos x         and          du = -sin x dx

 

then substitute them in:

 

1cos0cosπ/3(u)1/2(1u2)du

 

distribute and find the endpoints:

 

11/2(u1/2u)du

 

then power rule:

 

[23u3/212u2]and that should have a straight line at the end that means from one half to one, i just dont know how to do it on here.

Next just distribute that -1:

 

[23u3/2+12u2]once again there should be a line at the end that means from one half to one.

 

then use the fundamental theorem of calculus to find the definite integral:

 

[23(1)3/2+12(1)2][23(1/2)3/2+12(1/2)2]

 

then after some simplification I end up with:

 

23+12+23(122)18

 

then I get:

 

724+26

 

That is my answer, but the correct answer should be:

 

821+252168

 Feb 7, 2017

Best Answer 

 #2
avatar+26396 
+10

I have checked and rechecked my problem the whole way through and I can't figure out what is wrong with it, I would really really like to know what I did wrong.

0π/3(cosx)(sin3x)dx

 

Until 1cos0cosπ/3(u)1/2(1u2)du it is correct.

 

distribute and find the endpoints:

112u12(1u2) du=112(u12u12u2) du|u12u2 is not u!!!=112(u12u12+2) du=112(u12u12+42) du=112(u12u52) du=[23u3227u72)]112=[23u32+27u72)]112=23(1)+27(1)[23(12)32+27(12)72]=23+27+1321282|12=22=23+27+26256=14+621+5666562=821+503362=821+251682

 

 

laugh

 Feb 7, 2017
 #2
avatar+26396 
+10
Best Answer

I have checked and rechecked my problem the whole way through and I can't figure out what is wrong with it, I would really really like to know what I did wrong.

0π/3(cosx)(sin3x)dx

 

Until 1cos0cosπ/3(u)1/2(1u2)du it is correct.

 

distribute and find the endpoints:

112u12(1u2) du=112(u12u12u2) du|u12u2 is not u!!!=112(u12u12+2) du=112(u12u12+42) du=112(u12u52) du=[23u3227u72)]112=[23u32+27u72)]112=23(1)+27(1)[23(12)32+27(12)72]=23+27+1321282|12=22=23+27+26256=14+621+5666562=821+503362=821+251682

 

 

laugh

heureka Feb 7, 2017
 #3
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0

Ooohhh okay okay thank you heureka!!!!!! smiley

 Feb 7, 2017

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