Shayna
posted by Calculus .
Find the value of a so that the function f(x) = xe^(ax) has critical point at x = 9
I found that the derivative is axe^(ax)+e^(ax)
But I am not sure where to go from here?

e^(ax) (ax+1) = 0 for derivative = 0
so
a = 1/x
a = 1/9