Solve 10x + 9 = −81

The solution of 10x + 9 = −81 is x = -9.

10x + 9 = -81\ \Rightarrow\ x = -9

Explain it step by step in chat Make a short video of it

The lines y = 10x + 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
The goal is to get x alone. Undo the operations in the opposite order: first the addition, then the multiplication.
$10x + 9 = -81$
2
Subtract 9 from both sides:
$10x + 9 - 9 = -81 - 9 \ \Rightarrow\ 10x = -90$
3
Divide both sides by 10:
$\frac{10x}{10} = \frac{-90}{10} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$10\cdot(-9) + 9 = -90 + 9 = -81 \checkmark$

LaTeX source of the formulas on this page

\[ 10x + 9 = -81\ \Rightarrow\ x = -9 \]
\[ 10x + 9 = -81 \]
\[ 10x + 9 - 9 = -81 - 9 \ \Rightarrow\ 10x = -90 \]
\[ \frac{10x}{10} = \frac{-90}{10} \ \Rightarrow\ x = -9 \]
\[ 10\cdot(-9) + 9 = -90 + 9 = -81 \checkmark \]

Trying values of x in 10x + 9 = −81

x	10x + 9	Equals -81?
-11	-101	no
-10	-91	no
-9	-81	yes
-8	-71	no
-7	-61	no

Questions

What is x in 10x + 9 = −81?

The solution of 10x + 9 = −81 is x = -9.

How do you solve 10x + 9 = −81?

Subtract 9 from both sides to get 10x = -90, then divide both sides by 10 to get x = -9.

How do I check the answer?

Replace x by -9: 10(-9) + 9 = -81, which is -81.

Solve 10x + 9 = −81

How to work it out

Trying values of x in 10x + 9 = −81

Questions

Similar equations