Question

x² + 4x - 21 = 0 é igual a..

Answer 1

$x {}^{2} + 4x - 21 = 0 \\ x {}^{2} + 7x - 3x - 21 = 0 \\ x \: . \: (x + 7) - 3(x + 7) = 0 \\ (x + 7) \: . \: (x - 3) = 0 \\ x + 7 = 0 \\ \boxed{\boxed{\boxed{x = - 7}}} \\ x - 3 = 0 \\ \boxed{\boxed{\boxed{x = 3}}}$

att. yrz

Answer 2

Resposta:

S = { -7 , 3 }

Explicação passo-a-passo:

x² + 4x - 21 = 0

$x = \frac{ - b + - \sqrt{ {b}^{2} } - 4ac}{2a}$

$x = \frac{ - ( + 4) + - \sqrt{ {4}^{2} - 4.1. - 21} }{2.1}$

$x = \frac{ - 4 + - \sqrt{16 + 84} }{2}$

$x = \frac{ - 4 + - \sqrt{100} }{2}$

$x = \frac{ - 4 + - 10}{2}$

$x1 = \frac{ - 4 - 10}{2}$

$x1 = \frac{ - 14}{2}$

x' = - 7

$x2 = \frac{ - 4 + 10}{2}$

$x2 = \frac{6}{2}$

x'' = 3

S = { -7 , 3 }