2) -5,4x²=0
x²=0
x=0
3) x²-x-90=0
x²-x=90
x²-x+ 0,25=90+0,25
(x-0,5)²=90,25
x-0,5=9,5
x-0,5=-9,5
x1=10
x2= -8
4) 6x²-11x-52=0
6x²+13x-24x-52=0
(6x²+13x)-(24x-52)=0
x(6x+13)-4(6x+13)=0
(x-4)(6x+13)=0
x-4=0
6x+13=0
x1= 4
x2= -13/6
6) x²+15x=0
x(x+15)=0
x1=0
x+15=0
x2=-15
7) 14x²+9x+1=0
14x²+2x+7x+1=0
(14x²+2x)+(7x+1)=0
2x(7x+1)+(7x+1)=0
(2x+1)(7x+1)=0
2x+1=0
7x+1=0
x1= -0,5
x2= -1/7
8) x²-81=0
(x-9)(x+9)=0
x-9=0
x+9=0
x1=9
x2=-9