Pre-Algebra Examples

x^{2} + 4 x - 21 = 0

$x^{2} + 4 x - 21 = 0$

Step 1

Factor

x^{2} + 4 x - 21

$x^{2} + 4 x - 21$ using the AC method.

Tap for more steps...

Step 1.1

Consider the form

x^{2} + b x + c

$x^{2} + b x + c$ . Find a pair of integers whose product is

c

$c$ and whose sum is

b

$b$ . In this case, whose product is

- 21

$- 21$ and whose sum is

4

$4$ .

- 3, 7

$- 3, 7$

Step 1.2

Write the factored form using these integers.

(x - 3) (x + 7) = 0

$(x - 3) (x + 7) = 0$

(x - 3) (x + 7) = 0

$(x - 3) (x + 7) = 0$

Step 2

If any individual factor on the left side of the equation is equal to

0

$0$ , the entire expression will be equal to

0

$0$ .

x - 3 = 0

$x - 3 = 0$

x + 7 = 0

$x + 7 = 0$

Step 3

Set

x - 3

$x - 3$ equal to

0

$0$ and solve for

x

$x$ .

Tap for more steps...

Step 3.1

Set

x - 3

$x - 3$ equal to

0

$0$ .

x - 3 = 0

$x - 3 = 0$

Step 3.2

Add

3

$3$ to both sides of the equation.

x = 3

$x = 3$

x = 3

$x = 3$

Step 4

Set

x + 7

$x + 7$ equal to

0

$0$ and solve for

x

$x$ .

Tap for more steps...

Step 4.1

Set

x + 7

$x + 7$ equal to

0

$0$ .

x + 7 = 0

$x + 7 = 0$

Step 4.2

Subtract

7

$7$ from both sides of the equation.

x = - 7

$x = - 7$

x = - 7

$x = - 7$

Step 5

The final solution is all the values that make

(x - 3) (x + 7) = 0

$(x - 3) (x + 7) = 0$ true.

x = 3, - 7

$x = 3, - 7$