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Solução_Calculo_Stewart_6e

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F.<br />

TX.10<br />

CHAPTER 17 REVIEW ET CHAPTER 16 ¤ 301<br />

21. From the graph it appears that for points above the x-axis, vectors starting near a<br />

particular point are longer than vectors ending there, so divergence is positive.<br />

The opposite is true at points below the x-axis, where divergence is negative.<br />

F (x, y) = xy, x + y 2 ⇒ div F = ∂ (xy)+ ∂<br />

∂x ∂y x + y<br />

2<br />

= y +2y =3y.<br />

Thus div F > 0 for y>0,anddiv F < 0 for y

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