Solve 8x + 5 = 21

The solution of 8x + 5 = 21 is x = 2.

8x + 5 = 21\ \Rightarrow\ x = 2

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The lines y = 8x + 5 and y = 21 meet at x = 2. 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 addition, then the multiplication.
$8x + 5 = 21$
2
Subtract 5 from both sides:
$8x + 5 - 5 = 21 - 5 \ \Rightarrow\ 8x = 16$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{16}{8} \ \Rightarrow\ x = 2$
4
Check: put x = 2 back into the equation.
$8\cdot2 + 5 = 16 + 5 = 21 \checkmark$

LaTeX source of the formulas on this page

\[ 8x + 5 = 21\ \Rightarrow\ x = 2 \]
\[ 8x + 5 = 21 \]
\[ 8x + 5 - 5 = 21 - 5 \ \Rightarrow\ 8x = 16 \]
\[ \frac{8x}{8} = \frac{16}{8} \ \Rightarrow\ x = 2 \]
\[ 8\cdot2 + 5 = 16 + 5 = 21 \checkmark \]

Trying values of x in 8x + 5 = 21

x	8x + 5	Equals 21?
0	5	no
1	13	no
2	21	yes
3	29	no
4	37	no

Questions

What is x in 8x + 5 = 21?

The solution of 8x + 5 = 21 is x = 2.

How do you solve 8x + 5 = 21?

Subtract 5 from both sides to get 8x = 16, then divide both sides by 8 to get x = 2.

How do I check the answer?

Replace x by 2: 8(2) + 5 = 21, which is 21.

Solve 8x + 5 = 21

How to work it out

Trying values of x in 8x + 5 = 21

Questions

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