（11）原式=lim(x->1){[(1-x)(1-x)]/[(1+x^(1/2))(1+x^(1/3)+x^(2/3))(1-x)²]}(分子分母同乘(1+x^(1/2))(1+x^(1/3)+x^(2/3))，有理化分母)=lim(x->1){1/[(1+x^(1/2))(1+x^(1/3)+x^(2/3))]} (分子分母同除(1-x)²)=1/[(1+1)(1+1+1)]=1/6。
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