How Do You Integrate sin^6(x) Using Trigonometric Identities?

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To integrate sin^6(x), the problem is transformed into ∫(sin^2(x))^3 dx, leading to the expression (1/8)∫(1 - cos(2x))^3 dx. The discussion highlights the use of half-angle identities for cos^2(2x) and the challenge of integrating cos^3(2x). Suggestions include utilizing sine integral reduction formulas, which simplify the integration of powers of sine. The integration process continues until reaching sin^0(x), confirming the effectiveness of the reduction approach.
Stevecgz
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Problem:
\int sin^6 x dx
Progress so far:
\int (sin^2 x)^3 dx
\frac{1}{8} \int (1-cos2x)^3 dx
\frac 1 8 \int (1 - 3cos2x + 3cos^22x - cos^32x) dx

Any help is appreciated.

I can see using a half angle identity for cos^2(2x), but what do I do with the cos^3(2x)?


Steve
 
Last edited:
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Try looking up some sine integral reduction formulas on google. They take care of integrals involving powers of sine pretty nicely.
 
whozum said:
Try looking up some sine integral reduction formulas on google. They take care of integrals involving powers of sine pretty nicely.

I've found one in my text. Would I simply continue using the reduction formula until I get to sin^0(x)?

Steve
 
Yes that's pretty much how we did it.
 
Thanks whozum.

Steve
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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