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Solução_Calculo_Stewart_6e

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F.<br />

406 ¤ CHAPTER 9 DIFFERENTIAL EQUATIONS<br />

TX.10<br />

h = y(b) =a + 1 (cosh kb − 1). Sincecosh(kb) =cosh(−kb), there is no further information to extract from the<br />

k<br />

condition that y(b) =y(−b). However, we could replace a with the expression h − 1 (cosh kb − 1), obtaining<br />

k<br />

y = h + 1 (cosh kx − cosh kb). It would be better still to keep a in the expression for y, and use the expression for h to<br />

k<br />

solve for k in terms of a, b,andh. That would enable us to express y in terms of x and the given parameters a, b, andh.<br />

Sadly, it is not possible to solve for k in closed form. That would have to be done by numerical methods when specific<br />

parameter values are given.<br />

(b) The length of the cable is<br />

L = b<br />

<br />

1+(dy/dx)2 dx = b<br />

−b<br />

−b<br />

<br />

=2 (1/k)sinhkx =(2/k)sinhkb<br />

b<br />

0<br />

<br />

1+sinh 2 kx dx = b<br />

−b cosh kx dx =2 b<br />

0<br />

cosh kx dx

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