What is the x-intercept of: K(x)=x^3+2x^2-15. PLEASE. ?

Question

I have a TI-84 calculator, and for some reason, it's giving me a very hard time with this problem.

I have to find the:

x-intercept: ?

y-intercept: It said it's -15...is that right?

Local maximum?

Local minimums?

I solved another problem similar to this one but my calculator is driving me insane now, for some unknown reason...

PLEASE HELP ME.

Answer 1

K(x) = x^3 + 2x^2 - 15

Can't help you figure out the TI-84,

but your answers should be :

x-intercept = 1.948964810043268

y-intercept = -15 (do this by putting x = 0 in K(x))

For min/max, let derivative of K(x) = 0.

K '(x) = 3x^2 + 4x = 0

so, x(3x + 4) = 0 implies x = 0 or x = -4/3.

Local maximum is at x = -4/3

Local minimum is at x = 0