Solve 4x + 9 = 77

The solution of 4x + 9 = 77 is x = 17.

4x + 9 = 77\ \Rightarrow\ x = 17

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The lines y = 4x + 9 and y = 77 meet at x = 17. 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.
$4x + 9 = 77$
2
Subtract 9 from both sides:
$4x + 9 - 9 = 77 - 9 \ \Rightarrow\ 4x = 68$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{68}{4} \ \Rightarrow\ x = 17$
4
Check: put x = 17 back into the equation.
$4\cdot17 + 9 = 68 + 9 = 77 \checkmark$

LaTeX source of the formulas on this page

\[ 4x + 9 = 77\ \Rightarrow\ x = 17 \]
\[ 4x + 9 = 77 \]
\[ 4x + 9 - 9 = 77 - 9 \ \Rightarrow\ 4x = 68 \]
\[ \frac{4x}{4} = \frac{68}{4} \ \Rightarrow\ x = 17 \]
\[ 4\cdot17 + 9 = 68 + 9 = 77 \checkmark \]

Trying values of x in 4x + 9 = 77

x	4x + 9	Equals 77?
15	69	no
16	73	no
17	77	yes
18	81	no
19	85	no

Questions

What is x in 4x + 9 = 77?

The solution of 4x + 9 = 77 is x = 17.

How do you solve 4x + 9 = 77?

Subtract 9 from both sides to get 4x = 68, then divide both sides by 4 to get x = 17.

How do I check the answer?

Replace x by 17: 4(17) + 9 = 77, which is 77.

Solve 4x + 9 = 77

How to work it out

Trying values of x in 4x + 9 = 77

Questions

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