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Solve 2x + 9 = 21

The solution of 2x + 9 = 21 is x = 6.

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The lines y = 2x + 9 and y = 21 meet at x = 624681012101520253035x = 6y = 2x + 9y = 21
The lines y = 2x + 9 and y = 21 meet at x = 6. 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.

    2x+9=212x + 9 = 21
  2. 2

    Subtract 9 from both sides:

    2x+9−9=21−9 ⇒ 2x=122x + 9 - 9 = 21 - 9 \ \Rightarrow\ 2x = 12
  3. 3

    Divide both sides by 2:

    2x2=122 ⇒ x=6\frac{2x}{2} = \frac{12}{2} \ \Rightarrow\ x = 6
  4. 4

    Check: put x = 6 back into the equation.

    2⋅6+9=12+9=21✓2\cdot6 + 9 = 12 + 9 = 21 \checkmark
LaTeX source of the formulas on this page
\[ 2x + 9 = 21\ \Rightarrow\ x = 6 \]
\[ 2x + 9 = 21 \]
\[ 2x + 9 - 9 = 21 - 9 \ \Rightarrow\ 2x = 12 \]
\[ \frac{2x}{2} = \frac{12}{2} \ \Rightarrow\ x = 6 \]
\[ 2\cdot6 + 9 = 12 + 9 = 21 \checkmark \]

Trying values of x in 2x + 9 = 21

x2x + 9Equals 21?
417no
519no
621yes
723no
825no

Questions

What is x in 2x + 9 = 21?

The solution of 2x + 9 = 21 is x = 6.

How do you solve 2x + 9 = 21?

Subtract 9 from both sides to get 2x = 12, then divide both sides by 2 to get x = 6.

How do I check the answer?

Replace x by 6: 2(6) + 9 = 21, which is 21.

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    Solve 2x + 9 = 21: x = 6 (steps and check) | WordGPT