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Solve 9x + 15 = 78

The solution of 9x + 15 = 78 is x = 7.

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The lines y = 9x + 15 and y = 78 meet at x = 72468101220406080100120140x = 7y = 9x + 15y = 78
The lines y = 9x + 15 and y = 78 meet at x = 7. 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.

    9x+15=789x + 15 = 78
  2. 2

    Subtract 15 from both sides:

    9x+15−15=78−15 ⇒ 9x=639x + 15 - 15 = 78 - 15 \ \Rightarrow\ 9x = 63
  3. 3

    Divide both sides by 9:

    9x9=639 ⇒ x=7\frac{9x}{9} = \frac{63}{9} \ \Rightarrow\ x = 7
  4. 4

    Check: put x = 7 back into the equation.

    9⋅7+15=63+15=78✓9\cdot7 + 15 = 63 + 15 = 78 \checkmark
LaTeX source of the formulas on this page
\[ 9x + 15 = 78\ \Rightarrow\ x = 7 \]
\[ 9x + 15 = 78 \]
\[ 9x + 15 - 15 = 78 - 15 \ \Rightarrow\ 9x = 63 \]
\[ \frac{9x}{9} = \frac{63}{9} \ \Rightarrow\ x = 7 \]
\[ 9\cdot7 + 15 = 63 + 15 = 78 \checkmark \]

Trying values of x in 9x + 15 = 78

x9x + 15Equals 78?
560no
669no
778yes
887no
996no

Questions

What is x in 9x + 15 = 78?

The solution of 9x + 15 = 78 is x = 7.

How do you solve 9x + 15 = 78?

Subtract 15 from both sides to get 9x = 63, then divide both sides by 9 to get x = 7.

How do I check the answer?

Replace x by 7: 9(7) + 15 = 78, which is 78.

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    Solve 9x + 15 = 78: x = 7 (steps and check) | WordGPT