（a²-b²）x²+ab=(a²+b²)x
a^2(x²-x)-b²(x^2+x)+ab=0
a^2(x-1/2)^2-b²(x+1/2)^2+ab-1/4a^2+1/4b^2=0
a^2(x-1/2)^2-b²(x+1/2)^2+(1/2b+a)^2-5/4a^2=0