Solve 4x − 9 = −21

The solution of 4x − 9 = −21 is x = -3.

4x - 9 = -21\ \Rightarrow\ x = -3

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The lines y = 4x − 9 and y = -21 meet at x = -3. 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 subtraction, then the multiplication.
$4x - 9 = -21$
2
Add 9 to both sides:
$4x - 9 + 9 = -21 + 9 \ \Rightarrow\ 4x = -12$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{-12}{4} \ \Rightarrow\ x = -3$
4
Check: put x = -3 back into the equation.
$4\cdot(-3) - 9 = -12 - 9 = -21 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = -21\ \Rightarrow\ x = -3 \]
\[ 4x - 9 = -21 \]
\[ 4x - 9 + 9 = -21 + 9 \ \Rightarrow\ 4x = -12 \]
\[ \frac{4x}{4} = \frac{-12}{4} \ \Rightarrow\ x = -3 \]
\[ 4\cdot(-3) - 9 = -12 - 9 = -21 \checkmark \]

Trying values of x in 4x − 9 = −21

x	4x − 9	Equals -21?
-5	-29	no
-4	-25	no
-3	-21	yes
-2	-17	no
-1	-13	no

Questions

What is x in 4x − 9 = −21?

The solution of 4x − 9 = −21 is x = -3.

How do you solve 4x − 9 = −21?

Add 9 to both sides to get 4x = -12, then divide both sides by 4 to get x = -3.

How do I check the answer?

Replace x by -3: 4(-3) − 9 = -21, which is -21.

Solve 4x − 9 = −21

How to work it out

Trying values of x in 4x − 9 = −21

Questions

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