Explicație pas cu pas:
1)2x²+5x+2=0
2x²+4x+x+2=0
2x(x+2)+(x+2)=0
(x+2)(2x+1)=0,
x+2=0, x=-2
2x+1=0, x=-1/2
2) x²-12x+11=0
x²-x-11x+11=0
x(x-1)-11(x-1)=0
(x-1)(x-11)=0
x-1=0, x=1
x-11=0, x=11
3)x²+6x+9=0
x²+3x+3x+9=0
x(x+3)+3(x+3)=0
(x+3)(x+3)=0
x+3=0, x=-3