Solve 10x − 9 = 121

The solution of 10x − 9 = 121 is x = 13.

10x - 9 = 121\ \Rightarrow\ x = 13

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The lines y = 10x − 9 and y = 121 meet at x = 13. 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 subtraction, then the multiplication.
$10x - 9 = 121$
2
Add 9 to both sides:
$10x - 9 + 9 = 121 + 9 \ \Rightarrow\ 10x = 130$
3
Divide both sides by 10:
$\frac{10x}{10} = \frac{130}{10} \ \Rightarrow\ x = 13$
4
Check: put x = 13 back into the equation.
$10\cdot13 - 9 = 130 - 9 = 121 \checkmark$

LaTeX source of the formulas on this page

\[ 10x - 9 = 121\ \Rightarrow\ x = 13 \]
\[ 10x - 9 = 121 \]
\[ 10x - 9 + 9 = 121 + 9 \ \Rightarrow\ 10x = 130 \]
\[ \frac{10x}{10} = \frac{130}{10} \ \Rightarrow\ x = 13 \]
\[ 10\cdot13 - 9 = 130 - 9 = 121 \checkmark \]

Trying values of x in 10x − 9 = 121

x	10x − 9	Equals 121?
11	101	no
12	111	no
13	121	yes
14	131	no
15	141	no

Questions

What is x in 10x − 9 = 121?

The solution of 10x − 9 = 121 is x = 13.

How do you solve 10x − 9 = 121?

Add 9 to both sides to get 10x = 130, then divide both sides by 10 to get x = 13.

How do I check the answer?

Replace x by 13: 10(13) − 9 = 121, which is 121.

Solve 10x − 9 = 121

How to work it out

Trying values of x in 10x − 9 = 121

Questions

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