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S ψ(x, y) = (ψ1, ψ2, ψ3) = (x, y, f(x, y)) = (x, y, xy/2) <br />

<br />

dσ =<br />

⎛<br />

Jac ψ(x, y) = ⎝<br />

1 0<br />

0 1<br />

y/2 x/2<br />

2 <br />

2 <br />

<br />

det 2<br />

1 0<br />

0 1<br />

<br />

+ det 2<br />

<br />

1 0<br />

y/2 x/2<br />

⎞<br />

⎠<br />

<br />

+ det 2<br />

<br />

0 1<br />

y/2 x/2<br />

<br />

dx dy = 1 + x2 y2<br />

+ dx dy.<br />

4 4<br />

<br />

Jac ψ<br />

<br />

<br />

dσ = ∂xψ ∧ ∂yψ = − y<br />

<br />

<br />

<br />

, −x , 1 dx dy = 1 +<br />

2 2 x2<br />

4<br />

+ y2<br />

4<br />

<br />

<br />

<br />

Area(S) =<br />

S<br />

<br />

dσ =<br />

D<br />

<br />

1 + x2<br />

4<br />

+ y2<br />

4<br />

dx dy.<br />

<br />

1 <br />

dxdy = 4 + y2 + x2 dxdy.<br />

2 D<br />

x = ρ cos θ y = ρ sin θ <br />

ρ<br />

Area(S) =<br />

= π<br />

2<br />

2π<br />

0<br />

16<br />

4<br />

2 √ 3<br />

0<br />

√ t dt = π<br />

2<br />

<br />

1<br />

4 + ρ2 ρ dρ dθ = π<br />

2<br />

<br />

t 3/2<br />

3/2<br />

t=16<br />

t=4<br />

2 √ 3<br />

0<br />

= π<br />

56π<br />

(64 − 8) =<br />

3 3 .<br />

4 + ρ 2 ρ dρ = π<br />

2<br />

12<br />

0<br />

√ 4 + w dw<br />

S G(x, y, z) = z−f(x, y) = z−xy/2 <br />

G(x, y, z) = 0 <br />

± ∇G (−y/2, −x/2, 1) (−y, −x, 2)<br />

= ± = ± ,<br />

|∇G| |(−y/2, −x/2, 1)| x2 + y2 + 4<br />

<br />

ˆn(x, y, z) = (n1, n2, n3) =<br />

(−y, −x, 2)<br />

x 2 + y 2 + 4 ,

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