Solve 9x − 3 = 78

The solution of 9x − 3 = 78 is x = 9.

9x - 3 = 78\ \Rightarrow\ x = 9

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The lines y = 9x − 3 and y = 78 meet at x = 9. 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.
$9x - 3 = 78$
2
Add 3 to both sides:
$9x - 3 + 3 = 78 + 3 \ \Rightarrow\ 9x = 81$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{81}{9} \ \Rightarrow\ x = 9$
4
Check: put x = 9 back into the equation.
$9\cdot9 - 3 = 81 - 3 = 78 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 3 = 78\ \Rightarrow\ x = 9 \]
\[ 9x - 3 = 78 \]
\[ 9x - 3 + 3 = 78 + 3 \ \Rightarrow\ 9x = 81 \]
\[ \frac{9x}{9} = \frac{81}{9} \ \Rightarrow\ x = 9 \]
\[ 9\cdot9 - 3 = 81 - 3 = 78 \checkmark \]

Trying values of x in 9x − 3 = 78

x	9x − 3	Equals 78?
7	60	no
8	69	no
9	78	yes
10	87	no
11	96	no

Questions

What is x in 9x − 3 = 78?

The solution of 9x − 3 = 78 is x = 9.

How do you solve 9x − 3 = 78?

Add 3 to both sides to get 9x = 81, then divide both sides by 9 to get x = 9.

How do I check the answer?

Replace x by 9: 9(9) − 3 = 78, which is 78.

Solve 9x − 3 = 78

How to work it out

Trying values of x in 9x − 3 = 78

Questions

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