- #1
ianchenmu
- 10
- 0
Homework Statement
1) Suppose that [itex]f_k[/itex] is integrable on [itex] [a_k,\;b_k] [/itex] for [itex]k=1,...,n[/itex] and set [itex]R=[a_1,\;b_1]\times...\times[a_n,\;b_n] [/itex]. Prove that [itex]\int_{R}f_1(x_1)...f_n(x_n)d(x_1,...x_n)=(\int_{a_1}^{b_1}f_1(x_1)dx_1)...(\int_{a_n}^{b_n}f_n(x_n)dx_n) [/itex]
2)Compute the value of the improper integral:
[itex]I=\int_{\mathbb{R}}e^{-x^2}dx[/itex].
How to compute [itex]I \times I[/itex] and use Fubini and the change of variables formula?
3) Let [itex]E[/itex] be a nonempty Jordan region in [itex]\mathbb{R}^2[/itex] and [itex]f:E \rightarrow [0,\infty) [/itex] be integrable on [itex]E[/itex]. Prove that the volume of [itex]\Omega =\left \{ (x,y,z): (x,y) \in E,\;0\leq z\leq f(x,y)) \right \}[/itex] satisfies
[itex]Vol(\Omega)=\iint_{E}f\;dA[/itex].
Homework Equations
n/a
The Attempt at a Solution
For (2), how to compute [itex]I \times I[/itex] and use Fubini and the change of variables formula? Perhaps (2) is the easiest to start with... but I have little idea for (1) and (3)...So thank you for your help.
Last edited: