Answer:
x = - 7 or x = 3
Step-by-step explanation:
x² + 4x - 21 = 0
Using the quadratic formula which is
[tex]x = \frac{ - b \pm \sqrt{ {b}^{2} - 4ac } }{2a} \\ [/tex]
From the question
a = 1 , b = 4 , c = - 21
We have
[tex]x = \frac{ - 4 \pm \sqrt{ {4}^{2} - 4(1)( - 21)} }{2(1)} \\ = \frac{ - 4 \pm \sqrt{16 + 84} }{2} \\ = \frac{ - 4 \pm \sqrt{100} }{2} \: \: \: \: \: \: \: \\ = \frac{ - 4 \pm10 }{2} [/tex]
So we have
[tex]x = \frac{ - 4 - 10}{2} \: \: \: or \: \: \: \: x = \frac{ - 4 + 10}{2} \\ x = - \frac{14}{2} \: \: \: \: \: or \: x = \frac{6}{2} [/tex]
We have the final answer as
x = - 7 or x = 3
Hope this helps you
