Michael Corral: Vector Calculus

3.2 Double Integrals Over a General Region 109
Example 3.6. Evaluate
Solution:
∫ ∞ ∫ 1/x 2
1 0
∫ ∞ ∫ 1/x 2
1 0
2ydydx=
=
2ydydx.
∫ ∞
1
∫ ∞
1
(y 2∣ )
∣y=1/x ∣∣ 2
dx
y=0
x −4 dx=− 1 3 x−3∣ ∣ ∣∣
∞
1 = 0−(−1 3 )= 1 3
☛ ✟
✡Exercises
✠
A
For Exercises 1-6, evaluate the given double integral.
1.
3.
5.
7.
∫ 1 ∫ 1
0
∫ 2 ∫ lnx
1 0
∫ π/2 ∫ y
0 0
∫ 2 ∫ y
0
√ x
24x 2 ydydx 2.
0
4xdydx 4.
cosx sinydxdy 6.
1dxdy 8.
∫ π ∫ y
0 0
∫ 2 ∫ 2y
0 0
∫ ∞ ∫ ∞
0 0
∫ 1 ∫ x 2
0
0
sinxdxdy
e y2 dxdy
xye −(x2 +y 2) dxdy
2dydx
9. Find the volume V of the solid bounded by the three coordinate planes and the
plane x+y+z=1.
10. Find the volume V of the solid bounded by the three coordinate planes and the
plane 3x+2y+5z=6.
B
11. Explain why the double integral R
1dA gives the area of the region R. For simplicity,
you can assume that R is a region of the type shown in Figure 3.2.1(a).
C
12. Prove that the volume of a tetrahedron with mutually perpendicular
adjacent sides of lengths a, b, and c, as in Figure
3.2.6, is abc
6
. (Hint: Mimic Example 3.5, and recall from
Section 1.5 how three noncollinear points determine a plane.)
a
c
b
13. Show how Exercise 12 can be used to solve Exercise 10.
Figure 3.2.6