a) [tex] -x^{2}-4x-4 = 0
[/tex]
a = -1 b = -4 c = -4
Δ = [tex] b^{2}-4ac [/tex] = -4²-4(-1*(-4)) = 16-16 = 0
x₁,₂ = [tex] \frac{-b}{2a} = \frac{4}{-2} = -2[/tex]
b) -x²+2x-3 = 0
a=-1 b= 2 c=-3
Δ = b²-4ac = 2²-4(-1*(-3)) = 4-12= -8
Δ = solutie vida
c) -x²-x+5 = 0
a=-1 b=-1 c=5
Δ = b²-4ac = (-1)²-4(-1*5) = 1+20 = 21
x₁ = [tex] \frac{1+ \sqrt{21} }{-2} [/tex]
x₂ = [tex] \frac{1- \sqrt{21} }{-2} [/tex]
d) -x²+8x = 0
x(-x+8) = 0 ⇒[tex] \left \{ {{x=0} \atop {-x=-8}} \right. [/tex] ⇒[tex] \left \{ {{x=0} \atop {x=8}} \right. [/tex]
