AP CALCULUS: find open intervals of f(x) = x^3 - 12x

[joy08]

Hello. I need help finding the open intervals of this equation:

f(x)=3x^2-12. Here is the original equation: f(x)=x^3-12x

I already took the derivative of it by using the derivative test and I got 2,-2 as critical numbers. I got a large number when I plugged in the number. PLease help me. Thank you

 

[o_O]

Re: AP CALCULUS

What do you mean by "finding the open intervals of this equation"? What number and in what equation are you plugging into?

 

[stapel]

I need help finding the open intervals of this equation:

What does it mean to "find the open intervals" of an equation? Did you mean "equation", or did you mean "function"?

f(x)=3x^2-12. Here is the original equation: f(x)=x^3-12x

Since 3x[sup:6v5xjrlo]2[/sup:6v5xjrlo] - 12 does NOT equal x[sup:6v5xjrlo]3[/sup:6v5xjrlo] - 12x, why are you using the same name, "f(x)", for both?

I already took the derivative of it...

You took the derivative of which?

...by using the derivative test...

The First and Second Derivative Tests are tests which are applied to derivatives; they are not used to find derivatives. So what do you mean by the above?

...and I got 2,-2 as critical numbers.

Are these x-values? And of which function are they the critical numbers?

I got a large number when I plugged in the number.

You got what large number when you plugged which into where?

Please reply with a corrected statement of the exercise and its instructions, and a clear listing of your work and reasoning so far. Thank you!

Eliz.