Solve 4x − 11 = 21

The solution of 4x − 11 = 21 is x = 8.

4x - 11 = 21\ \Rightarrow\ x = 8

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The lines y = 4x − 11 and y = 21 meet at x = 8. 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.
$4x - 11 = 21$
2
Add 11 to both sides:
$4x - 11 + 11 = 21 + 11 \ \Rightarrow\ 4x = 32$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{32}{4} \ \Rightarrow\ x = 8$
4
Check: put x = 8 back into the equation.
$4\cdot8 - 11 = 32 - 11 = 21 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 11 = 21\ \Rightarrow\ x = 8 \]
\[ 4x - 11 = 21 \]
\[ 4x - 11 + 11 = 21 + 11 \ \Rightarrow\ 4x = 32 \]
\[ \frac{4x}{4} = \frac{32}{4} \ \Rightarrow\ x = 8 \]
\[ 4\cdot8 - 11 = 32 - 11 = 21 \checkmark \]

Trying values of x in 4x − 11 = 21

x	4x − 11	Equals 21?
6	13	no
7	17	no
8	21	yes
9	25	no
10	29	no

Questions

What is x in 4x − 11 = 21?

The solution of 4x − 11 = 21 is x = 8.

How do you solve 4x − 11 = 21?

Add 11 to both sides to get 4x = 32, then divide both sides by 4 to get x = 8.

How do I check the answer?

Replace x by 8: 4(8) − 11 = 21, which is 21.

Solve 4x − 11 = 21

How to work it out

Trying values of x in 4x − 11 = 21

Questions

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