# Curve Sketching stuck

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• Mar 8th 2011, 03:12 PM
bradycat
Curve Sketching stuck
Hi,
Stuck on curve sketching on the following.
y = x^5 -5x

You have part A which is finding the x-intercepts when y=0. I found x=0 and x= +and- 1.495.
IS THIS CORRECT??? please check

Then Part b is min/max when y'=0
y'=5x^4-5

5(x^4-1)=0
5=0 CANT USE........... then X= ROOT of 1 comes to x= - or + 1????
Then to solve for Y it s x= 1,-4 and x= -1,4 ???

Part C is pts of inflection y''=0
So it's y"=20x^3
How to solve for X???

Can some one direct me in the right direction, thanks
Joanne(Headbang)
• Mar 8th 2011, 03:22 PM
pickslides
Quote:

Originally Posted by bradycat
Then Part b is min/max when y'=0
y'=5x^4-5

$\displaystyle y'=0$

$\displaystyle 5x^4-5=0$

$\displaystyle 5x^4=5$

$\displaystyle x^4=\frac{5}{5}$

$\displaystyle x^4=1$

$\displaystyle x=\sqrt[4]{1} = \pm1$
• Mar 9th 2011, 02:20 PM
bradycat
I got it, thanks.