Question

X² + 4x - 21 = 0 answer and solution? please help me ​

Answer 1

x = - 7 or x = 3

Explanation:

x² + 4x - 21 = 0

Using the quadratic formula which is

`x = \frac{ - b \pm \sqrt{ {b}^(2) - 4ac } }{2a} \\`

From the question

a = 1 , b = 4 , c = - 21

We have

`x = \frac{ - 4 \pm \sqrt{ {4}^(2) - 4(1)( - 21)} }{2(1)} \\ = ( - 4 \pm √(16 + 84) )/(2) \\ = ( - 4 \pm √(100) )/(2) \: \: \: \: \: \: \: \\ = ( - 4 \pm10 )/(2)`

So we have

`x = ( - 4 - 10)/(2) \: \: \: or \: \: \: \: x = ( - 4 + 10)/(2) \\ x = - (14)/(2) \: \: \: \: \: or \: x = (6)/(2)`

We have the final answer as

x = - 7 or x = 3

Hope this helps you

Answer 2

x = -7, 3

General Formulas and Concepts:

Order of Operations: BPEMDAS

Standard Form: ax² + bx + c = 0

• Factoring

Explanation:

Step 1: Define

x² + 4x - 21 = 0

Step 2: Solve for x

1. Factor: (x - 3)(x + 7) = 0
2. Find roots: x = -7, 3

Step 3: Check

Plug in x to verify it's a solution.

1. Substitute: (-7)² + 4(-7) - 21 = 0
2. Exponents: 49 + 4(-7) - 21 = 0
3. Multiply: 49 - 28 - 21 = 0
4. Combine like terms: 0 = 0

1. Substitute: (3)² + 4(3) - 21 = 0
2. Exponents: 9 + 4(3) - 21 = 0
3. Multiply: 9 + 12 - 21 = 0
4. Combine like terms: 0 = 0