Step 1: Linearize (sinx)3 using Euler's formula.
We know that sinx=2ieix−e−ix.
Therefore, (sinx)3=(2ieix−e−ix)3.
Expand the numerator using the binomial expansion (a−b)3=a3−3a2b+3ab2−b3:
(eix−e−ix)3=(eix)3−3(eix)2(e−ix)+3(eix)(e−ix)2−(e−ix)3
=ei3x−3ei2xe−ix+3eixe−i2x−e−i3x
=ei3x−3eix+3e−ix−e−i3x
Group terms to form sine functions:
=(ei3x−e−i3x)−3(eix−e−ix)
Using the identity eiθ−e−iθ=2isinθ:
=2isin(3x)−3(2isinx)
Now substitute this back into the expression for (sinx)3:
(sinx)3=(2i)32isin(3x)−6isinx
=−8i2i(sin(3x)−3sinx)
=−4sin(3x)−3sinx
=−41sin(3x)+43sinx
So, the linearized form is:
(sinx)3=43sinx−41sin(3x)
Step 2: Calculate the integral I=∫02π(sinx)3dx using the linearized form.
Substitute the linearized expression into the integral:
I=∫02π(43sinx−41sin(3x))dx
Integrate term by term:
I=43∫02πsinxdx−41∫02πsin(3x)dx
The antiderivative of sinx is −cosx.
The antiderivative of sin(3x) is −31cos(3x).
I=[−43cosx−41(−31cos(3x))]02π
I=[−43cosx+121cos(3x)]02π
Step 3: Evaluate the definite integral.
Evaluate the expression at the upper limit x=2π:
(−43cos(2π)+121cos(3⋅2π))=(−43⋅0+121⋅0)=0
Evaluate the expression at the lower limit x=0:
(−43cos(0)+121cos(3⋅0))=(−43⋅1+121⋅1)=−43+121
To combine these, find a common denominator, which is 12:
−43+121=−129+121=−128=−32
Subtract the lower limit value from the upper limit value:
I=0−(−32)=32
The final answer is \boxed{\frac{2{3}}}.
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