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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 7] The Areas of Plane Figures 153<br />

Sec. 7. The Areas of Plane Figures<br />

1. Area <strong>in</strong> rectangular coord<strong>in</strong>ates. If a cont<strong>in</strong>uous curve is def<strong>in</strong>ed <strong>in</strong><br />

rectangular coord<strong>in</strong>ates by the equation y f(x) [f(x)^Q], the area of the<br />

curvil<strong>in</strong>ear trapezoid bounded by this curve, by two vertical l<strong>in</strong>es at the<br />

a b X<br />

Fig. 40<br />

po<strong>in</strong>ts x a and x = 6 and by a segment of the jc-axis<br />

is given by the formula b<br />

(Fig. 40),<br />

Example 1. Compute the area bounded by the parabola y = -~ the<br />

straight l<strong>in</strong>es x = \ and .v 3, and the x-axis<br />

^<br />

(Fig. 41).<br />

y-fi(*)<br />

Fig. 42 Fig. 43<br />

Solution. The sought-for area is expressed by the <strong>in</strong>tegral<br />

b X<br />

X<br />

(1)

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