The function \(f\) is defined by \(f(x) = \frac{2}{(x+2)^2}\) for \(x > -2\).
(a) Find \(\int_{1}^{\infty} f(x) \, dx\).
(b) The equation of a curve is such that \(\frac{dy}{dx} = f(x)\). It is given that the point \((-1, -1)\) lies on the curve.
Find the equation of the curve.
Solution
(a) To find \(\int_{1}^{\infty} f(x) \, dx\), we first integrate \(f(x) = \frac{2}{(x+2)^2}\).
The integral of \(\frac{2}{(x+2)^2}\) is \(\frac{-2}{x+2}\).
Evaluate the definite integral from 1 to \(\infty\):
\(\left[ \frac{-2}{x+2} \right]_1^{\infty} = 0 - \left( \frac{-2}{3} \right) = \frac{2}{3}\).
(b) Given \(\frac{dy}{dx} = \frac{2}{(x+2)^2}\), integrate to find \(y\):
\(y = \frac{-2}{x+2} + c\).
Using the point \((-1, -1)\), substitute \(x = -1\) and \(y = -1\):
\(-1 = \frac{-2}{-1+2} + c\).
\(-1 = -2 + c\).
\(c = 1\).
Thus, the equation of the curve is \(y = \frac{-2}{x+2} + 1\).
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