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Solve 4x + 9 = 21

The solution of 4x + 9 = 21 is x = 3.

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The lines y = 4x + 9 and y = 21 meet at x = 3-224681020304050x = 3y = 4x + 9y = 21
The lines y = 4x + 9 and y = 21 meet at x = 3. 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.

    4x+9=214x + 9 = 21
  2. 2

    Subtract 9 from both sides:

    4x+9−9=21−9 ⇒ 4x=124x + 9 - 9 = 21 - 9 \ \Rightarrow\ 4x = 12
  3. 3

    Divide both sides by 4:

    4x4=124 ⇒ x=3\frac{4x}{4} = \frac{12}{4} \ \Rightarrow\ x = 3
  4. 4

    Check: put x = 3 back into the equation.

    4⋅3+9=12+9=21✓4\cdot3 + 9 = 12 + 9 = 21 \checkmark
LaTeX source of the formulas on this page
\[ 4x + 9 = 21\ \Rightarrow\ x = 3 \]
\[ 4x + 9 = 21 \]
\[ 4x + 9 - 9 = 21 - 9 \ \Rightarrow\ 4x = 12 \]
\[ \frac{4x}{4} = \frac{12}{4} \ \Rightarrow\ x = 3 \]
\[ 4\cdot3 + 9 = 12 + 9 = 21 \checkmark \]

Trying values of x in 4x + 9 = 21

x4x + 9Equals 21?
113no
217no
321yes
425no
529no

Questions

What is x in 4x + 9 = 21?

The solution of 4x + 9 = 21 is x = 3.

How do you solve 4x + 9 = 21?

Subtract 9 from both sides to get 4x = 12, then divide both sides by 4 to get x = 3.

How do I check the answer?

Replace x by 3: 4(3) + 9 = 21, which is 21.

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    Solve 4x + 9 = 21: x = 3 (steps and check) | WordGPT