Solve 6x + 9 = −21

The solution of 6x + 9 = −21 is x = -5.

6x + 9 = -21\ \Rightarrow\ x = -5

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The lines y = 6x + 9 and y = -21 meet at x = -5. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

1
The goal is to get x alone. Undo the operations in the opposite order: first the addition, then the multiplication.
$6x + 9 = -21$
2
Subtract 9 from both sides:
$6x + 9 - 9 = -21 - 9 \ \Rightarrow\ 6x = -30$
3
Divide both sides by 6:
$\frac{6x}{6} = \frac{-30}{6} \ \Rightarrow\ x = -5$
4
Check: put x = -5 back into the equation.
$6\cdot(-5) + 9 = -30 + 9 = -21 \checkmark$

LaTeX source of the formulas on this page

\[ 6x + 9 = -21\ \Rightarrow\ x = -5 \]
\[ 6x + 9 = -21 \]
\[ 6x + 9 - 9 = -21 - 9 \ \Rightarrow\ 6x = -30 \]
\[ \frac{6x}{6} = \frac{-30}{6} \ \Rightarrow\ x = -5 \]
\[ 6\cdot(-5) + 9 = -30 + 9 = -21 \checkmark \]

Trying values of x in 6x + 9 = −21

x	6x + 9	Equals -21?
-7	-33	no
-6	-27	no
-5	-21	yes
-4	-15	no
-3	-9	no

Questions

What is x in 6x + 9 = −21?

The solution of 6x + 9 = −21 is x = -5.

How do you solve 6x + 9 = −21?

Subtract 9 from both sides to get 6x = -30, then divide both sides by 6 to get x = -5.

How do I check the answer?

Replace x by -5: 6(-5) + 9 = -21, which is -21.

Solve 6x + 9 = −21

How to work it out

Trying values of x in 6x + 9 = −21

Questions

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