Solve 9 − 9x = −72
Linear equation, worked out line by line the way a teacher would write it.
Answer
| Solution | x = 9 |
Step-by-step solution
5 steps-
1 Given9 - 9 x = -72
Solve for x.
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2 Subtract 9 from both sides
An equation stays true as long as you do the same thing to both sides, like adding the same weight to both pans of a balance. Adding or subtracting the same amount on both sides moves a term to the other side, where it appears with the opposite sign.
- 9 x = -81Move the constant terms to the right.
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3 Divide both sides by -9
Dividing both sides by -9 undoes the multiplication by -9, so the variable is left on its own. Both sides change in the same way, so the equation stays true (dividing by 0 is the one thing that is never allowed).
x = \frac{-81}{-9} -
4 Simplifyx = 9
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5 Check\begin{aligned}x = 9:\quad -72 = -72\quad\checkmark\end{aligned}
Substituting each solution back makes both sides equal.
Check by substitution
| x | Left side | Right side | |
|---|---|---|---|
| 9 | −72 | −72 | ✓ |
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