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Solve 8x + 9 = 81

The solution of 8x + 9 = 81 is x = 9.

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The lines y = 8x + 9 and y = 81 meet at x = 9468101214406080100120x = 9y = 8x + 9y = 81
The lines y = 8x + 9 and y = 81 meet at x = 9. 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.

    8x+9=818x + 9 = 81
  2. 2

    Subtract 9 from both sides:

    8x+9−9=81−9 ⇒ 8x=728x + 9 - 9 = 81 - 9 \ \Rightarrow\ 8x = 72
  3. 3

    Divide both sides by 8:

    8x8=728 ⇒ x=9\frac{8x}{8} = \frac{72}{8} \ \Rightarrow\ x = 9
  4. 4

    Check: put x = 9 back into the equation.

    8⋅9+9=72+9=81✓8\cdot9 + 9 = 72 + 9 = 81 \checkmark
LaTeX source of the formulas on this page
\[ 8x + 9 = 81\ \Rightarrow\ x = 9 \]
\[ 8x + 9 = 81 \]
\[ 8x + 9 - 9 = 81 - 9 \ \Rightarrow\ 8x = 72 \]
\[ \frac{8x}{8} = \frac{72}{8} \ \Rightarrow\ x = 9 \]
\[ 8\cdot9 + 9 = 72 + 9 = 81 \checkmark \]

Trying values of x in 8x + 9 = 81

x8x + 9Equals 81?
765no
873no
981yes
1089no
1197no

Questions

What is x in 8x + 9 = 81?

The solution of 8x + 9 = 81 is x = 9.

How do you solve 8x + 9 = 81?

Subtract 9 from both sides to get 8x = 72, then divide both sides by 8 to get x = 9.

How do I check the answer?

Replace x by 9: 8(9) + 9 = 81, which is 81.

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    Solve 8x + 9 = 81: x = 9 (steps and check) | WordGPT