Solve 2x − 5 = 21

The solution of 2x − 5 = 21 is x = 13.

2x - 5 = 21\ \Rightarrow\ x = 13

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The lines y = 2x − 5 and y = 21 meet at x = 13. 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.
$2x - 5 = 21$
2
Add 5 to both sides:
$2x - 5 + 5 = 21 + 5 \ \Rightarrow\ 2x = 26$
3
Divide both sides by 2:
$\frac{2x}{2} = \frac{26}{2} \ \Rightarrow\ x = 13$
4
Check: put x = 13 back into the equation.
$2\cdot13 - 5 = 26 - 5 = 21 \checkmark$

LaTeX source of the formulas on this page

\[ 2x - 5 = 21\ \Rightarrow\ x = 13 \]
\[ 2x - 5 = 21 \]
\[ 2x - 5 + 5 = 21 + 5 \ \Rightarrow\ 2x = 26 \]
\[ \frac{2x}{2} = \frac{26}{2} \ \Rightarrow\ x = 13 \]
\[ 2\cdot13 - 5 = 26 - 5 = 21 \checkmark \]

Trying values of x in 2x − 5 = 21

x	2x − 5	Equals 21?
11	17	no
12	19	no
13	21	yes
14	23	no
15	25	no

Questions

What is x in 2x − 5 = 21?

The solution of 2x − 5 = 21 is x = 13.

How do you solve 2x − 5 = 21?

Add 5 to both sides to get 2x = 26, then divide both sides by 2 to get x = 13.

How do I check the answer?

Replace x by 13: 2(13) − 5 = 21, which is 21.

Solve 2x − 5 = 21

How to work it out

Trying values of x in 2x − 5 = 21

Questions

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