Stuart Grant
01/17/2024 · Junior High School
a) \( \int_{-2}^{0} x^{2} e^{x^{3} / 2} d x \)
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Tutor-Verified Answer
Step-by-step Solution
To evaluate the integral
\[
I = \int_{-2}^{0} x^{2} e^{x^{3} / 2} \, dx,
\]
we can use integration by parts. We will let:
- \( u = e^{x^{3}/2} \) (which we will differentiate)
- \( dv = x^2 \, dx \) (which we will integrate)
First, we need to compute \( du \) and \( v \):
1. Differentiate \( u \):
\[
du = \frac{d}{dx} e^{x^{3}/2} \, dx = e^{x^{3}/2} \cdot \frac{3}{2} x^2 \, dx.
\]
2. Integrate \( dv \):
\[
v = \int x^2 \, dx = \frac{x^3}{3}.
\]
Now we apply integration by parts, which states:
\[
\int u \, dv = uv - \int v \, du.
\]
Substituting our expressions for \( u \), \( v \), \( du \), and \( dv \):
\[
I = \left[ e^{x^{3}/2} \cdot \frac{x^3}{3} \right]_{-2}^{0} - \int_{-2}^{0} \frac{x^3}{3} \cdot \left( e^{x^{3}/2} \cdot \frac{3}{2} x^2 \right) \, dx.
\]
Evaluating the boundary term:
At \( x = 0 \):
\[
e^{0} \cdot \frac{0^3}{3} = 0.
\]
At \( x = -2 \):
\[
e^{(-2)^{3}/2} \cdot \frac{(-2)^3}{3} = e^{-4} \cdot \frac{-8}{3} = -\frac{8}{3} e^{-4}.
\]
Thus, the boundary term evaluates to:
\[
0 - \left(-\frac{8}{3} e^{-4}\right) = \frac{8}{3} e^{-4}.
\]
Now we need to evaluate the integral:
\[
\int_{-2}^{0} \frac{x^3}{3} \cdot \left( e^{x^{3}/2} \cdot \frac{3}{2} x^2 \right) \, dx = \frac{1}{2} \int_{-2}^{0} x^5 e^{x^{3}/2} \, dx.
\]
Thus, we have:
\[
I = \frac{8}{3} e^{-4} - \frac{1}{2} \int_{-2}^{0} x^5 e^{x^{3}/2} \, dx.
\]
Let’s denote
\[
J = \int_{-2}^{0} x^5 e^{x^{3}/2} \, dx.
\]
Now we can express \( I \) in terms of \( J \):
\[
I = \frac{8}{3} e^{-4} - \frac{1}{2} J.
\]
To evaluate \( J \), we can again use integration by parts. Let:
- \( u = e^{x^{3}/2} \)
- \( dv = x^5 \, dx \)
Following similar steps as before, we find:
1. \( du = e^{x^{3}/2} \cdot \frac{3}{2} x^2 \, dx \)
2. \( v = \frac{x^6}{6} \)
Thus,
\[
J = \left[ e^{x^{3}/2} \cdot \frac{x^6}{6} \right]_{-2}^{0} - \int_{-2}^{0} \frac{x^6}{6} \cdot \left( e^{x^{3}/2} \cdot \frac{3}{2} x^2 \right) \, dx.
\]
Evaluating the boundary term:
At \( x = 0 \):
\[
e^{0} \cdot \frac{0^6}{6} = 0.
\]
At \( x = -2 \):
\[
e^{-4} \cdot \frac{(-2)^6}{6} = e^{-4} \cdot \frac{64}{6} = \frac{32}{3} e^{-4}.
\]
Thus, the boundary term evaluates to:
\[
0 - \frac{32}{3}
Quick Answer
The integral \( \int_{-2}^{0} x^{2} e^{x^{3} / 2} \, dx \) can be evaluated using integration by parts, resulting in an expression involving \( e^{-4} \) and another integral \( J \). The final result is a combination of these terms.
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