lim(x->0) [(x+1)^1/2-1] /x=lim(x->0) [(x+1)^1/2 -1] *[(x+1)^1/2 +1] / x *[(x+1)^1/2 +1]=lim(x->0) (x+1 -1) / x *[(x+1)^1/2 +1]=lim(x->0) 1 / [(x+1)^1/2 +1] 代入x=0= 1/(1+1)= 1/2