a) x² - 9 = 0
x² = 9
x = ±3
x' = -3
x" = 3
b) x² + 8x = 0
x × (x + 8) = 0
x = 0
x + 8 = 0
x' = 0
x" = -8
c) x² + 5x + 4 = 0
Δ = 5² - 4×1×4
Δ = 25 - 16
Δ = 9
[tex]x= \frac{-5+-\sqrt{9} }{2.1}[/tex]
[tex]x= \frac{-5+-3}{2}[/tex]
[tex]x'=\frac{-5-3}{2}[/tex]
[tex]x"=\frac{-5+3}{2}[/tex]
[tex]x' = -4\\x" = -1[/tex]
