x²+3x=t
(t+1)(t+3)=-1
t²+3t++t+3+1=0
t²+4t+4=0
D1=4-4=0
t=-2
x²+3x=-2
x²+3x+2=0
D=9-8=1
x1=(-3+1)/2=-1 x2=(-3-1)/2=-2
