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 subtraction, then the multiplication.
$6x - 9 = 21$
2
Add 9 to 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.
$6\cdot5 - 9 = 30 - 9 = 21 \checkmark$

LaTeX source of the formulas on this page

\[ 6x - 9 = 21\ \Rightarrow\ x = 5 \]
\[ 6x - 9 = 21 \]
\[ 6x - 9 + 9 = 21 + 9 \ \Rightarrow\ 6x = 30 \]
\[ \frac{6x}{6} = \frac{30}{6} \ \Rightarrow\ x = 5 \]
\[ 6\cdot5 - 9 = 30 - 9 = 21 \checkmark \]

Trying values of x in 6x − 9 = 21

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

Add 9 to 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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