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Solve 3x + 15 = 9

The solution of 3x + 15 = 9 is x = -2.

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The lines y = 3x + 15 and y = 9 meet at x = -2-8-6-4-224-10-551015202530x = -2y = 3x + 15y = 9
The lines y = 3x + 15 and y = 9 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. 1

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

    3x+15=93x + 15 = 9
  2. 2

    Subtract 15 from both sides:

    3x+15−15=9−15 ⇒ 3x=−63x + 15 - 15 = 9 - 15 \ \Rightarrow\ 3x = -6
  3. 3

    Divide both sides by 3:

    3x3=−63 ⇒ x=−2\frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2
  4. 4

    Check: put x = -2 back into the equation.

    3⋅(−2)+15=−6+15=9✓3\cdot(-2) + 15 = -6 + 15 = 9 \checkmark
LaTeX source of the formulas on this page
\[ 3x + 15 = 9\ \Rightarrow\ x = -2 \]
\[ 3x + 15 = 9 \]
\[ 3x + 15 - 15 = 9 - 15 \ \Rightarrow\ 3x = -6 \]
\[ \frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2 \]
\[ 3\cdot(-2) + 15 = -6 + 15 = 9 \checkmark \]

Trying values of x in 3x + 15 = 9

x3x + 15Equals 9?
-43no
-36no
-29yes
-112no
015no

Questions

What is x in 3x + 15 = 9?

The solution of 3x + 15 = 9 is x = -2.

How do you solve 3x + 15 = 9?

Subtract 15 from both sides to get 3x = -6, then divide both sides by 3 to get x = -2.

How do I check the answer?

Replace x by -2: 3(-2) + 15 = 9, which is 9.

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    Solve 3x + 15 = 9: x = -2 (steps and check) | WordGPT