f(1) = 5, 所以x^2f(1) = 5x^2
lim x->1, 所以x^2=1, f(x^2)= f(1) = 5

x^2f(1) - f(x^2) = 5x^2 -5
5x^2 - 5 = 5(x^2 - 1) = 5(x-1)(x+1)
所以, [x^2f(1) - f(x^2)]/[x-1] when lim x->1 = [5(x-1)(x+1)]/[x-1] when lim x->1 = [5(x+1)] when lim x->1

apply x->1, 5(x+1) = 5(2) = 10

答案應該是10, 詳細理論還要請其他高人解釋

如有錯請多多包含