Question

Resolva as equações (U = Reais)

a) x² + 9x + 20 = 0

Answer 1

Aplicando a fórmula do Delta, onde:

$a=1,~b=9,~c=20 \\ \\ \Delta~=b^2-4.a.c \\ \Delta~=9^2-4.1.20 \\ \Delta~=81-80 \\ \Delta~=1$

Agora, jogando na fórmula de Bháskara:

$x= \frac{-b\pm \sqrt{\Delta~}}{2.a} \\ \\ x= \frac{-9\pm \sqrt{1}}{2.1} \\ \\ x= \frac{-9\pm1}{2}$

$x'= \frac{-9+1}{2}= \frac{-8}{2}=-4 \\ \\ x''= \frac{-9-1}{2}= \frac{-10}{2}=-5 \\ \\ \\ S=\{-5,~-4\}$

:))