Originally Posted by

**Jayde** Sorry if I posted this in the wrong place.

Two numbers x and y are such that 2x + y = 12.

The product P is formed by multiplying the first number by the square of the second number so that P = xy²

P = 4x³ - 48x² + 144x

I worked out the two values of x for which dP/dx = 0

They are x = 6 and x = 2 (hopefully!)

Now it says : The values of x and y must both be positive, show that there is only one value of x for which P is stationary.

How do I do this?

Please and thank you x