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16 MULTIPLE INTEGRALS

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CHAPTER <strong>16</strong><br />

SAMPLE EXAM SOLUTIONS<br />

(a)<br />

(b) The Jacobian is<br />

∂x/∂u ∂x/∂v<br />

∣<br />

∣∣ ∂y/∂u ∂y/∂v ∣<br />

∫∫S (3x + 2y) dA = ∫ 1<br />

0<br />

= 3 ∫ 1<br />

0<br />

∣∣ ∣∣∣ ∣∣∣<br />

∣ = 2 1<br />

1 2 ∣∣ = 3, so<br />

∫ 1<br />

0<br />

[3 (2u + v) + 2 (u + 2v)] 3 du dv<br />

[<br />

1<br />

3u 2 + 3uv + u 2 + 4uv] dv<br />

0<br />

= 3 ∫ 1<br />

0 (3 + 3v + 1 + 4v) dv = 3 [<br />

4v + 7 2 v2] 1<br />

0 = 45 2<br />

<strong>16</strong>.<br />

∫ 9<br />

1<br />

17. (a)<br />

∫ π/2 ∫ π/4<br />

0 π/6 ρ2 sin φ dφ dθ dρ = π 2<br />

=<br />

∫ 9 [<br />

1 −ρ 2 cos φ ] π/4<br />

[<br />

13<br />

ρ 3] 9<br />

√<br />

3 −<br />

√<br />

2<br />

2<br />

π/6 dρ = π 2<br />

= 182<br />

1<br />

3<br />

∫ √ √ 9 3 − 2<br />

1<br />

( √3<br />

−<br />

√<br />

2<br />

)<br />

π<br />

2<br />

ρ 2 dρ<br />

T maps the unit square in the uv-plane to the unit circle in the xy-plane.<br />

(b) The area of S is π.<br />

∫ 1 ∫ 1 ∫ 1<br />

−1 −1<br />

(ax + by) dydx<br />

−1<br />

2ax dx<br />

18. f ave = ∫ 1 ∫ 1<br />

−1 −1 1 dydx =<br />

= 0<br />

4<br />

939

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