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Use integration by parts to find recursion formulas, expressing the given integral in terms of an integral with a lower power:

• Show that [math]\int x^ne^xdx = x^ne^x - n\int x^{n-1}e^xdx[/math].
• Show that [math]\int \sec^nx \; dx = \frac{\sec^{n-2}x \tan x}{n-1} + \frac{n-2}{n-1} \int \sec^{n-2} x \; dx[/math].
• Find a reduction formula, expressing [math]\int(\ln |ax + b|)^n dx[/math] in terms of [math]\int(\ln|ax + b|)^{n-1}dx[/math].