1) Let's solve that quadratic equation x²-4x -5 =0
2)For this equation, let's choose another method.
Let's solve this factorizing it, since a =1
Which two addends whose sum is equal to -4?
S= -5 +1 = -4
Which two factors whose product is equal to -5?
P = -5 x 1 = -5
Because we can rewrite that equation
x² -4x -5 =0
(x +1) (x+5) =0
So the roots are
(x +1)
x +1 =0
x= -1
(x+5)
x+5=0
x=5
S={-1,5}