# Double absolute value equations.

I'm self-studying Cambridge IGCSE additional maths and I've got to the double absolute value equations but I've been really struggling to understand how it works for a while now.

My textbook gives an example of an equation and how to solve it as shown below.

$\left | x+4 \right | +\left | x-5 \right | = 11 $

$\left | x+4 \right |= 11 -\left | x-5 \right | $

$x+4 = 11 -\left | x-5 \right |$ (1)

$x+4 = \left | x-5 \right |-11$ (2)

Using equation (1)

$\left | x-5 \right | = 7-x$

$ x-5 = 7-x$

$2x = 12$

$x=6$

Or

$x-5=-(7-x)$

$0=-2$ Which is false

Using equation (2)

$\left | x-5 \right |=x+15$

$x-5=x+15$

$0=20$ which is false

or

$ x-5=-(x+15)$

$2x=-10$

$x=-5$

The solution is $x=6$ or $x=-5$

I know how to solve an equation like

$\left | x+5 \right |= \left | x-4 \right |$

I just don't understand what is happening here. Could you help explain it step by step why each step is taken and if possible could you graph it so that I can visually see what is happening?

Thanks for the help.

## Answer

**Answers can be viewed only if**

- The questioner was satisfied and accepted the answer, or
- The answer was disputed, but the judge evaluated it as 100% correct.

- answered
- 1360 views
- $10.00

### Related Questions

- Prove that $1+\frac{1}{\sqrt{2}}+\dots+\frac{1}{\sqrt{n}} \leq 2 \sqrt{n}-1$
- Module isomorphism and length of tensor product.
- Fields and Galois theory
- Algebra Word Problem #2
- Absolute value functions.
- Compounding interest of principal P, where a compounding withdrawal amount W get withdrawn from P before each compounding of P.
- Linearly independent vector subsets.
- Algorithm for printing @ symbols