Expert: Ahmed Salami - 11/30/2010

Question
Find the value of x for which the given function is increasing and those values of x for which it is decreasing.
y= x^2+2x my text book answer is Inc.x>-1, dec.x=-1 ,but how do you do this step by step. thanks  

Answer
Hi Ken,
A function is increasing when its derivative is positive and decreasing when the derivative is negative.
y = x² + 2x
dy/dx = 2x + 2
The function is therefore increasing when 2x + 2 > 0
2x > -2
x > -1
and decreasing when 2x + 2 < 0
2x < -2
x < -1

Regards