Question

Help! Absolute value equations

Answer 1

4. k = -2 or k = -5

6. m = 5 or m = -21

Explanation:

Here is the rule:

To solve an absolute value equation, get the absolute value alone on one side. Then split it into two equations separated by the word or. Each equation has what is inside the absolute value on the left side, and on the right side, one equation has the right side of the absolute value equation, and the other equation has the negative of the right side of the absolute equation.

This is a long explanation which is easier to understand with an example.

Example:

|3x + 2| = 16

Split it into two equations separated by the word "or."

3x + 2 = 16 or 3x + 2 = -16

You see that the left side of the two equations is the inside of the absolute value. The right side of the two equations is positive and negative 16 as explained int he rule.

4.

3 = |2k + 7|

Switch sides.

|2k + 7| = 3

Follow the rule above and split the equation into two equations separated by the word "or."

2k + 7 = 3 or 2k + 7 = -3

2k = -4 or 2k = -10

k = -2 or k = -5

6.

3|m + 8| = 39

We want the absolute value alone on the left side, so divide both sides by 3.

|m + 8| = 13

Now apply the rule above to split the equation into two equations.

m + 8 = 13 or m + 8 = -13

m = 5 or m = -21

Answer 2

• k = -5 , k= -2
• m= -21 , m=5

Explanation:

4.

`3=\left|2k+7\right|\\\\\mathrm{Switch\:sides}\\\left|2k+7\right|=3\\\\\mathrm{Apply\:absolute\:rule}:\quad \\\mathrm{If}\:|u|\:=\:a,\:a>0\:\mathrm{then}\:u\:=\:a\:\quad \mathrm{or}\quad \:u\:=\:-a\\\\2k+7=-3\quad \mathrm{or}\quad \:2k+7=3\\\\2k+7=-3\quad :\quad k=-5\\\\2k+7=3\quad :\quad k=-2\\\\\mathrm{Combine\:Solutions:}\\k=-5\quad \mathrm{or}\quad \:k=-2`

6.

`3\left|m+8\right|=39\\\mathrm{Divide\:both\:sides\:by\:}3\\(3\left|m+8\right|)/(3)=(39)/(3)\\\\Simplify\\\left|m+8\right|=13\\\\\mathrm{Apply\:absolute\:rule}:\quad \\\mathrm{If}\:|u|\:=\:a,\:a>0\:\mathrm{then}\:u\:=\:a\:\quad \mathrm{or}\quad \:u\:=\:-a\\\\m+8=-13\quad \mathrm{or}\quad \:m+8=13\\\\m+8=-13\quad :\quad m=-21\\m+8=13\quad :\quad m=5\\\\\mathrm{Combine\:Solutions:}\\m=-21\quad \mathrm{or}\quad \:m=5`