Absolute Value Equations #1

Algebra Level 1

Given that

5 x + 6 + 2 = 6 x 3 , \large |5x+6|+2=6x-3,

find the value of x x .

This problem is part of the set Absolute Value Equations .


The answer is 11.

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4 solutions

Tan Yong Boon
Oct 25, 2014

l5x+6l + 2= 6x - 3

Since absolute value is either a positive number or 0 and in this case, x cannot equal 0,

l5x+6l + 2 = 6x - 3 becomes 5x+6 + 2 = 6x - 3

And after solving this equation, we obtain x=11.

How do we know 5 x + 6 5x+6 is necessarily a positive number in this case, without finding out the value of x x ?

Jared Low - 6 years, 4 months ago
Roger Erisman
May 15, 2015

You must also consider that the value inside the absval could be a negative number.

So, -(5x + 6) = 6x - 5 ======>x = - 1/11 and substituting into initial equation shows that that solution is invalid. Only x = 11 works.

you completed above solution

Sarith Imaduwage - 5 years, 3 months ago

5 x + 6 + 2 = 6 x 3 { For x < 6 5 5 x 6 + 2 = 6 x 3 x = 1 11 6 5 rejected For x 6 5 5 x + 6 + 2 = 6 x 3 x = 11 > 6 5 accepted |5x+6| + 2 = 6x - 3 \implies \begin{cases} \text{For }x < - \dfrac 65 & \implies - 5x - 6 + 2 = 6x - 3 & \implies x = - \dfrac 1{11} \not < - \dfrac 65 \color{#D61F06} \text{ rejected} \\ \text{For }x \ge - \dfrac 65 & \implies 5x + 6 + 2 = 6x - 3 & \implies x = \boxed{11} > - \dfrac 65 \color{#3D99F6} \text{ accepted} \end{cases}

Reymond Adlawan
Nov 18, 2014

l5x+6l + 2 = 6x - 3 becomes 5x+6 + 2 = 6x - 3 after that used the addition property of equalities then it will become 6x-5x = 3+6+2 perform the equation x=11 then check it to the original equation ;)

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