Question

Equação de 2 grau

7²+14×-21=0

Answer 1

$\sf 7 {x}^{2} + 14x - 21 = 0$

$\sf \Delta = {b}^{2} - 4ac$

$\sf \Delta = {14}^{2} - 4\cdot 7\cdot ( - 21)$

$\sf \Delta = 196 - 4\cdot 7\cdot ( - 21)$

$\sf \Delta = 196 + 588$

$\sf \Delta = 784$

$\sf x_{½} = \dfrac{ - b \pm \sqrt{\Delta} }{2a}$

$\sf x_{½} = \dfrac{ - 14 \pm \sqrt{784} }{2\cdot 7}$

$\sf x_{½} = \dfrac{ - 14 \pm 28 }{14}$

$\sf \red{x_{1} = \dfrac{ - 14 - 28 }{ 14} = \dfrac{ - 42}{ \: \: \: \: 14} = - 3}$

$\sf\red{ x_{2} = \dfrac{ - 14 + 28 }{ 14} = \dfrac{ 14}{ 14} = 1}$