Question

Rezolvati ecuatia -x^2-7x+8=0
(cu delta).

Answer 1

$- {x}^{2} - 7x + 8 = 0 \: | \times ( - 1)$

${x}^{2} + 7x - 8 = 0$

$a = 1$

$b = 7$

$c = - 8$

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

$\Delta = {7}^{2} - 4 \times 1 \times ( - 8)$

$\Delta = 49 + 32$

$\Delta = 81$

$x_{1,2}=\frac{-b\pm\sqrt{\Delta}}{2a}$

$x_{1,2}=\frac{-7\pm\sqrt{81}}{2 \times 1}$

$x_{1,2}=\frac{-7\pm9}{2}$

$x_{1}=\frac{-7 + 9}{2} = \frac{2}{2} = 1$

$x_{2}=\frac{-7 - 9}{2} = - \frac{16}{2} = - 8$