Solve 7x − 9 = 40

The solution of 7x − 9 = 40 is x = 7.

7x - 9 = 40\ \Rightarrow\ x = 7

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The lines y = 7x − 9 and y = 40 meet at x = 7. 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.
$7x - 9 = 40$
2
Add 9 to both sides:
$7x - 9 + 9 = 40 + 9 \ \Rightarrow\ 7x = 49$
3
Divide both sides by 7:
$\frac{7x}{7} = \frac{49}{7} \ \Rightarrow\ x = 7$
4
Check: put x = 7 back into the equation.
$7\cdot7 - 9 = 49 - 9 = 40 \checkmark$

LaTeX source of the formulas on this page

\[ 7x - 9 = 40\ \Rightarrow\ x = 7 \]
\[ 7x - 9 = 40 \]
\[ 7x - 9 + 9 = 40 + 9 \ \Rightarrow\ 7x = 49 \]
\[ \frac{7x}{7} = \frac{49}{7} \ \Rightarrow\ x = 7 \]
\[ 7\cdot7 - 9 = 49 - 9 = 40 \checkmark \]

Trying values of x in 7x − 9 = 40

x	7x − 9	Equals 40?
5	26	no
6	33	no
7	40	yes
8	47	no
9	54	no

Questions

What is x in 7x − 9 = 40?

The solution of 7x − 9 = 40 is x = 7.

How do you solve 7x − 9 = 40?

Add 9 to both sides to get 7x = 49, then divide both sides by 7 to get x = 7.

How do I check the answer?

Replace x by 7: 7(7) − 9 = 40, which is 40.

Solve 7x − 9 = 40

How to work it out

Trying values of x in 7x − 9 = 40

Questions

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