Question

Equações do segundo grau , sendo U=R
a - x² - 7= 0
b - x ² + 5x = 0
c - 4x² - 9x= 0
d - 3 x² + 5x = 0

Answer 1

$A)~~ x^{2} -7=0\to\\ x^{2} =7\to\\ x=\pm~ \sqrt{7} \\\\ \boxed{S=\{-\sqrt{7}~;\sqrt{7}\}}$


Todas as demais, vou fazer colocando x em evidência:



$B)~~ x^{2} +5x=0\to\\\\ x(x+5)=0\\\\ x=0\\\\ x+5=0\to~~x=-5 \\\\\\ \boxed{S=\{-5~;~0\}}$



$C)~~4 x^{2} -9x=0\to\\\\ x(4x-9)=0\to\\\\ x=0\\\\ 4x-9=0\to~~4x=9\to~~x= \dfrac{9}{4} \\\\\\ \boxed{S=\left\{0~;~\frac{9}{4}\right\}}$



$D)~~ 3 x^{2} +5x=0\to\\\\ x(3x+5)=0\to\\\\ x=0\\\\ 3x+5=0\to ~~ 3x=-5\to~~x=- \dfrac{5}{3} \\\\\\ \boxed{S=\left\{ - \dfrac{5}{3} ~;~0 \right\}}$