lim(x->∞) [√(x^2-x+1) -ax-b ]=0
lim(x->∞) [(x^2-x+1) -(ax+b)^2 ]/[√(x^2-x+1) +ax+b ]=0
lim(x->∞) [(1-a)x^2-(1+2ab)x+(1-b^2) ]/[√(x^2-x+1) +ax+b ]=0
lim(x->∞) [(1-a)x-(1+2ab)+(1-b^2)/x ]/[√(1-1/x+1/x^2) +a+b/x ]=0
分子: x
=>
1-a =0
a=1
1+2ab =0
1+2b=0
b=-1/2