If the gradient of the curve $y=2k{{x}^{2}}+x+1$ at x =  1 is 9. Find k 

If the volume of hemisphere is increasing at a steady rate of 18πm³s^–1 . At what rate is its radius changing when it is 6m

If $y=2x\cos 2x-\sin 2x$, find $\frac{dy}{dx}$when $x=\tfrac{\pi }{4}$ 

A trader realizes 10 – x² naira profit from the sales of x bags of corns. How many bags will give him maximum profit.