absolute functions help

**skatefallen15** · September 19th 2010, 09:55 AM

This problem was proposed to me recently and the absolute values are throwing me off.

Given the functions f(x) = |-2x-4| and g(x) = |x+3|, considering appropriate domain restrictions, state the defining equations for the three regions of the function (f+g)(x).

Obviously the solution will be a piecewise function, but I'm having trouble getting the equations for the three regions of the function(f+g)(x). Absolute signs can be tricky!

**skeeter** · September 19th 2010, 10:20 AM

Originally Posted by skatefallen15

This problem was proposed to me recently and the absolute values are throwing me off.

Given the functions f(x) = |-2x-4| and g(x) = |x+3|, considering appropriate domain restrictions, state the defining equations for the three regions of the function (f+g)(x).

Obviously the solution will be a piecewise function, but I'm having trouble getting the equations for the three regions of the function(f+g)(x). Absolute signs can be tricky!

case 1 ...

$(-2x-4) \ge 0$ and $(x+3) \ge 0$

$-2(x+2) \ge 0$ ... $x \ge -3$

$x+2 \le 0$

$x \le -2$

intersection is the interval $[-3,-2]$

case 2 ...

$(-2x-4) \ge 0$ and $(x+3) < 0$

$x \le -2$ ... $x < -3$

intersection is $(-\infty,-3)$

case 3 ...

$(-2x-4) < 0$ and $(x+3) \ge 0$

$-2(x+2) < 0$ ... $x \ge -3$

$x+2 > 0$

$x > -2$

intersection is $(-2,\infty)$

case 4 ...

$(-2x-4) < 0$ and $(x+3) < 0$

$x > -2$ ... $x < -3$

no intersection.

so ... the three regions are $(-\infty,-3)$ , $[-3,-2]$ , and $(-2,\infty)$

I'll leave you to define $(f+g)(x)$ for each region.