(1)2x 2 -7x+5=0, b 2 -4ac=(-7) 2 -4×2×5=9, x=
x 1 =1,x 2 =
(2)3x 2 -10x-5=0, 3x 2 -10x=5, x 2 -
配方得:x 2 -
(x-
开方得:x-
x 1 =
(3)2x(x-3)=9-3x, 2x(x-3)+3(x-9)=0, (x-3)(2x+3)=0, x-3=0,2x+3=0, x 1 =3,x 2 =-
(4)(x-5)(x+2)=8, x 2 -3x-18=0, (x-6)(x+3)=0, x-6=0,x+3=0, x 1 =6,x 2 =-3. |