part b and c 毛蟲入毛(b) f_n = c_n (a constant function), and {c_n} does not converge (c) 我估類似由 x^ + 1 慢慢畫堆parabolaapproach到變 |x|, 唔肯定 (我諗緊點寫個explicit formula出黎 )
part b and c 毛蟲入毛