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Solve 12x + 9 = 21

The solution of 12x + 9 = 21 is x = 1.

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The lines y = 12x + 9 and y = 21 meet at x = 1-4-2246-60-40-2020406080100x = 1y = 12x + 9y = 21
The lines y = 12x + 9 and y = 21 meet at x = 1. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

  1. 1

    The goal is to get x alone. Undo the operations in the opposite order: first the addition, then the multiplication.

    12x+9=2112x + 9 = 21
  2. 2

    Subtract 9 from both sides:

    12x+9−9=21−9 ⇒ 12x=1212x + 9 - 9 = 21 - 9 \ \Rightarrow\ 12x = 12
  3. 3

    Divide both sides by 12:

    12x12=1212 ⇒ x=1\frac{12x}{12} = \frac{12}{12} \ \Rightarrow\ x = 1
  4. 4

    Check: put x = 1 back into the equation.

    12⋅1+9=12+9=21✓12\cdot1 + 9 = 12 + 9 = 21 \checkmark
LaTeX source of the formulas on this page
\[ 12x + 9 = 21\ \Rightarrow\ x = 1 \]
\[ 12x + 9 = 21 \]
\[ 12x + 9 - 9 = 21 - 9 \ \Rightarrow\ 12x = 12 \]
\[ \frac{12x}{12} = \frac{12}{12} \ \Rightarrow\ x = 1 \]
\[ 12\cdot1 + 9 = 12 + 9 = 21 \checkmark \]

Trying values of x in 12x + 9 = 21

x12x + 9Equals 21?
-1-3no
09no
121yes
233no
345no

Questions

What is x in 12x + 9 = 21?

The solution of 12x + 9 = 21 is x = 1.

How do you solve 12x + 9 = 21?

Subtract 9 from both sides to get 12x = 12, then divide both sides by 12 to get x = 1.

How do I check the answer?

Replace x by 1: 12(1) + 9 = 21, which is 21.

Similar equations

    Solve 12x + 9 = 21: x = 1 (steps and check) | WordGPT