Y = |x+1|-1

1. May 13, 2010

weedannycool

if i have an equation of a graph and it had a modulus in it. how do i find where it crosses the x and y axis. From what i know inside the modulus is alway positive.

y=|x+1|-1

2. May 13, 2010

HallsofIvy

Re: modulus

If "inside the modulus is alway positive", that is, if x+ 1> 0, then |x+ 1|= x+ 1 and so your equation becomes y= x+ 1- 1= x. The graph of y= x is the straight line passing through (0, 0).

If, however, you only meant that the modulus (absolute value) is never negative (it can be 0), then you need to break the problem into two parts: If x< -1, then x+1< 0 and so |x+ 1|= -(x+1). For x< -1, y= |x+1|- 1= -x- 1- 1= -x- 2. That crosses the x-axis when -x- 2= 0 or when x= -2 which is less that -1 so one x-intercept is at x= -2. The "y- intercept" occurs when x= 0 which does not satisfy x< -1.

If $x\ge -1$ then $x+ 1\ge 0$ and so |x+ 1|= x+ 1. NOW we have y= |x+1|- 1= x+ 1=1 = x which crosses the x-axis and y-axis at (0,0).

The x-intercepts are x= -2 and x= 0 and the y-intercept is y= 0.

3. May 13, 2010

weedannycool

Re: modulus

thank you. i was meaning that the abosolute value is never negative.

great help.