1) -(x²-6x+9)=0
-(x-3)²=0
(x-3)²=0
|x-3|=0
x-3=0
x=3
2)x²+16=0
x²= -16
√x² = √-16
|x|= -4 => x= 4i ∧ x= -4i
3)5x² +3x=0
x(5x+3)=0
x=0 ∧ 5x+3=0
5x= -3
x= -3/5
4)x² -8x +12=0
x²-8x+16 -4=0
(x-4)²-4=0
[(x-4)-2][(x-4)+2]=0
(x-4-2)(x-4+2)=0
(x-6)(x-2)=0
x-6= 0 ∧ x-2=0
x= 6 x=2
5)x² +x +5= 0
a=1
b=1
c=5
x= (-1 +/- √ 1-4*5)/2= (-1 +/- √1-20)/2= (-1 +/- √19)/2
