# Maxima and Minima Problem

1. Jan 11, 2005

Hello all

Given $$y = -x^4 + 18x^2 + 11$$ how would you find the intervals where the function is increasing and decreasing? Would you have to find $$f'(x)$$ and find critical points?

Thanks

2. Jan 11, 2005

### Galileo

Yep, that's the most straightforward and surefire way to do it.

3. Jan 11, 2005

### marlon

yes that is the way to go...

make a sign chart of the first derivative and you'll have all the info you need

marlon

4. Jan 11, 2005

### dextercioby

Due to the biquadratic character of the function,the resulting 3-rd order equation (when setting the first derivative to zero) can be solved easily.
One of the solutions is zero and is a local minimum.

Daniel.