Solve 4x − 9 = 51

The solution of 4x − 9 = 51 is x = 15.

4x - 9 = 51\ \Rightarrow\ x = 15

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The lines y = 4x − 9 and y = 51 meet at x = 15. 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.
$4x - 9 = 51$
2
Add 9 to both sides:
$4x - 9 + 9 = 51 + 9 \ \Rightarrow\ 4x = 60$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{60}{4} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$4\cdot15 - 9 = 60 - 9 = 51 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = 51\ \Rightarrow\ x = 15 \]
\[ 4x - 9 = 51 \]
\[ 4x - 9 + 9 = 51 + 9 \ \Rightarrow\ 4x = 60 \]
\[ \frac{4x}{4} = \frac{60}{4} \ \Rightarrow\ x = 15 \]
\[ 4\cdot15 - 9 = 60 - 9 = 51 \checkmark \]

Trying values of x in 4x − 9 = 51

x	4x − 9	Equals 51?
13	43	no
14	47	no
15	51	yes
16	55	no
17	59	no

Questions

What is x in 4x − 9 = 51?

The solution of 4x − 9 = 51 is x = 15.

How do you solve 4x − 9 = 51?

Add 9 to both sides to get 4x = 60, then divide both sides by 4 to get x = 15.

How do I check the answer?

Replace x by 15: 4(15) − 9 = 51, which is 51.

Solve 4x − 9 = 51

How to work it out

Trying values of x in 4x − 9 = 51

Questions

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