The gradient of the curve $=\frac{a}{x}+bx^2$ at the point (3,6) is 7. Calculate the values of a and b.
I did it,
$6=\frac{a}{3}+b(3^2) \tag{1} $ We also have: (derivative) $y'=-\frac{a}{x^2}+2bx \tag{2}$
$7=-\frac{a}{3^2}+2b(3) \tag{3} $
but it doesn't seen right.
the answer is a=-9, b=1
Can you help me out? thanks.