Find the maximum or minimum value of function and the value of x when it occurs: -2x^2+5x+5.

Answer 1

let y = -x^2 + 5x + 5
dy/dx = -2x + 5
= 0 for a max of y

2x = 5
x = 5/2

when x = 5/2
y = -25/4 + 5(5/2) + 5
= 45/4

you should recognize y = -x^2 + 5x + 5 as a downward opening parabola ,
the max is 45/4 when x = 5/2

Answer 2

but the answer says that it's a max of 65/8 at x=5/4

Answer 3

Correct. Reiny missed the -2x^2. Even experts trip over the details sometimes.

Answer 4

so can you show me the correct way to do it?

Answer 5

wait nvm thanks for your help :D