To solve the integral ∫02πe2xcos(3x)dx, we will again use integration by parts.
Recall that integration by parts is given by:
∫udv=uv−∫vdu
First, let's choose u and dv:
u=e2xanddv=cos(3x)dx
Now, compute du and v:
du=2e2xdxandv=31sin(3x)
Applying integration by parts:
∫e2xcos(3x)dx=e2x⋅31sin(3x)−∫31sin(3x)⋅2e2xdx=31e2xsin(3x)−32∫e2xsin(3x)dx
Now, we need to integrate ∫e2xsin(3x)dx. We use integration by parts again for this integral. Let:
u=e2xanddv=sin(3x)dx
Then:
du=2e2xdxandv=−31cos(3x)
Applying integration by parts again:
∫e2xsin(3x)dx=−31e2xcos(3x)−∫−31cos(3x)⋅2e2xdx=−31e2xcos(3x)+32∫e2xcos(3x)dx
Notice that we end up with the original integral ∫e2xcos(3x)dx on the right-hand side. Let's call this integral I:
I=∫e2xcos(3x)dx
So we have:
I=31e2xsin(3x)−32(−31e2xcos(3x)+32∫e2xcos(3x)dx)I=31e2xsin(3x)+92e2xcos(3x)−94I
Now we solve for I:
I+94I=31e2xsin(3x)+92e2xcos(3x)913I=31e2xsin(3x)+92e2xcos(3x)I=139(31e2xsin(3x)+92e2xcos(3x))I=133e2xsin(3x)+132e2xcos(3x)
Now we need to evaluate this expression from 0 to 2π:
(133e2xsin(3x)+132e2xcos(3x))02π
Evaluating at the bounds:
=(133e2⋅2πsin(3⋅2π)+132e2⋅2πcos(3⋅2π))−(133e0sin(0)+132e0cos(0))=(133eπsin(23π)+132eπcos(23π))−(133⋅0+132⋅1)=(133eπ⋅(−1)+132eπ⋅0)−132=(−133eπ)−132=−133eπ−132=−131(3eπ+2)
So the value of the integral is:
−131(3eπ+2)
Would you like more details or have any questions?
Here are some related questions:
How do you integrate by parts?
What are some common mistakes when applying integration by parts?
How can we verify the result of an integral?
What are the properties of exponential functions?
How do trigonometric functions behave over different intervals?
What are some applications of definite integrals?
How can substitution simplify integrals?
What are some techniques for integrating products of functions?
Tip: When using integration by parts, choosing u and dv wisely can simplify the process significantly.
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Integration by parts Exponential functions Trigonometric functions