Question

Resolva mentalmente as equações abaixo, determinando suas raízes A) X²+2x-3=0 B)X²-15x+26=0 C) X²-15x+36=0 D) X²+16x-36=0

Answer 1

a)∆=4-4•1•(-3)
∆=4+12
∆=16
x'=-2+4/2= 2/2= 1.
x"=-2-4/2= -6/2= -3.

b)∆=225-104
∆=121
x'=15+11/2= 26/2= 13.
x"=15-11/2= 4/2= 2.

c)∆=225-144
∆=81
x'=15+9/2= 24/2= 12.
x"=15-9/2= 6/2= 3.

d)∆=256+144
∆=400.
x'=-16+20/2= 4/2=2.
x"=-16-20/2= -36/2= -18.