Let y = y(x) be the solution of the differential equation dydx + 2x (1 + x2 )2y = xe 1 (1 + x2 ); y(0) = 0. Then the area enclosed by the curve f(x) = y(x)e- 1 (1 + x2 ) and the line y - x = 4 is .
Answer
18
Solution
Linear D.E.: 2x(1 + x2)2 dx = - 11 + x2 I.F. = e-1/(1 + x2)
y e-1/(1 + x2) = x e1/(1 + x2) e-1/(1 + x2) dx = x22 + C
y(0) = 0 C = 0 f(x) = y(x) e-1/(1 + x2) = x22
With y = x + 4: x22 = x + 4 x2 - 2x - 8 = 0 x = -2, 4
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Area = -24 (x + 4 - x22 )dx = [ x22 + 4x - x36 ]-24
= 403 - (- 143 ) = 18
Answer: 18