（3x+5）（3x-5）+6x=-26
9x^2-25+6x=-26
9x^2+6x+1=0
(3x+1)^2=0
3x+1=0
x=-1/3
2y^2+4y-3
=2y^2+4y+2-5
=2(y^2+2y+1)-5
=2(y+1)^2-5