Х²+4х-21=0

To solve the quadratic equation х² + 4х - 21 = 0, we can use the quadratic formula. The quadratic formula is given by:

x = (-b ± √(b² - 4ac)) / (2a)

In this equation, a is the coefficient of х², b is the coefficient of х, and c is the constant term.

Comparing this equation to our given equation х² + 4х - 21 = 0, we can see that a = 1, b = 4, and c = -21.

Now, substituting these values into the quadratic formula, we have:

x = (-4 ± √(4² - 4 * 1 * -21)) / (2 * 1)

Simplifying further:

x = (-4 ± √(16 + 84)) / 2

x = (-4 ± √100) / 2

x = (-4 ± 10) / 2

Now we have two possible solutions:

1. x = (-4 + 10) / 2 = 6 / 2 = 3

2. x = (-4 - 10) / 2 = -14 / 2 = -7

So, the solutions to the quadratic equation х² + 4х - 21 = 0 are x = 3 and x = -7.