Question

Suppose y=3x-7 and x>=0. Then, the minimum value of (x^2)*y is?,and the maximum value of (x^2)*y is?

I don't know the answer.But my answer is -1372/243 and 0,is that right?

Answer 1

`MIN(-1372/242,14/9)`,`MAX(0;0)`

Explanation:

Consider
`f(x)=3x^3-7x^2`
then we get
`f'(x)=9x^2-14x`
`f''(x)=18x-14`
And
`f'(x)=0` if `x=0` or `x=14/9`
then we obtain
`f''(0)=-14<0`
`f''(14/9)=14>0`