Solve 4x − 9 = 15

The solution of 4x − 9 = 15 is x = 6.

4x - 9 = 15\ \Rightarrow\ x = 6

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The lines y = 4x − 9 and y = 15 meet at x = 6. 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.
$4x - 9 = 15$
2
Add 9 to both sides:
$4x - 9 + 9 = 15 + 9 \ \Rightarrow\ 4x = 24$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{24}{4} \ \Rightarrow\ x = 6$
4
Check: put x = 6 back into the equation.
$4\cdot6 - 9 = 24 - 9 = 15 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = 15\ \Rightarrow\ x = 6 \]
\[ 4x - 9 = 15 \]
\[ 4x - 9 + 9 = 15 + 9 \ \Rightarrow\ 4x = 24 \]
\[ \frac{4x}{4} = \frac{24}{4} \ \Rightarrow\ x = 6 \]
\[ 4\cdot6 - 9 = 24 - 9 = 15 \checkmark \]

Trying values of x in 4x − 9 = 15

x	4x − 9	Equals 15?
4	7	no
5	11	no
6	15	yes
7	19	no
8	23	no

Questions

What is x in 4x − 9 = 15?

The solution of 4x − 9 = 15 is x = 6.

How do you solve 4x − 9 = 15?

Add 9 to both sides to get 4x = 24, then divide both sides by 4 to get x = 6.

How do I check the answer?

Replace x by 6: 4(6) − 9 = 15, which is 15.

Solve 4x − 9 = 15

How to work it out

Trying values of x in 4x − 9 = 15

Questions

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