Solve 4x + 15 = −21

The solution of 4x + 15 = −21 is x = -9.

4x + 15 = -21\ \Rightarrow\ x = -9

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

The lines y = 4x + 15 and y = -21 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.
$4x + 15 = -21$
2
Subtract 15 from both sides:
$4x + 15 - 15 = -21 - 15 \ \Rightarrow\ 4x = -36$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{-36}{4} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$4\cdot(-9) + 15 = -36 + 15 = -21 \checkmark$

LaTeX source of the formulas on this page

\[ 4x + 15 = -21\ \Rightarrow\ x = -9 \]
\[ 4x + 15 = -21 \]
\[ 4x + 15 - 15 = -21 - 15 \ \Rightarrow\ 4x = -36 \]
\[ \frac{4x}{4} = \frac{-36}{4} \ \Rightarrow\ x = -9 \]
\[ 4\cdot(-9) + 15 = -36 + 15 = -21 \checkmark \]

Trying values of x in 4x + 15 = −21

x	4x + 15	Equals -21?
-11	-29	no
-10	-25	no
-9	-21	yes
-8	-17	no
-7	-13	no

Questions

What is x in 4x + 15 = −21?

The solution of 4x + 15 = −21 is x = -9.

How do you solve 4x + 15 = −21?

Subtract 15 from both sides to get 4x = -36, then divide both sides by 4 to get x = -9.

How do I check the answer?

Replace x by -9: 4(-9) + 15 = -21, which is -21.

Solve 4x + 15 = −21

How to work it out

Trying values of x in 4x + 15 = −21

Questions

Similar equations