（1）-2x^2+13-15=0
(-2x-3)(x+5)=0
x=-3/2 x=-5
(2)x^2=2√2x-2
x^2-2√2x+2=0
(x- √2)^2=0
x= √2
(3）(2/3)x^2-（1/6）x=1/2
4x^2-x-3=0
(4x+3)(x-1)=0
x=-3/4 x=1