跟我学昆曲:199*(1-2/1)*(-3/1)*(-4/1)*.........*(1-199-/1)=?

199*(1-2/1)*(-3/1)*(-4/1)*.........*(1-199-/1)=? 1/1x2+1/2x3+1/3x4+...+1/199x200,帮帮我啊 1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+100) 1+1/1+2+1/1+2+3+......+1/1+2+3+......+10 (1/2005-1)(1/2004-1)........(1/3-1)(1/2-1) (1-1/2^2)(1-1/3^2)....(1-1/10^2) (1-1/2^2)(1-1/3^2)....(1-1/10^2) 3/2=2+1/1*2=1/1+1/2 1/1*2+1/2*3+1/3*4+...+1/2000*2001 1/(1*2)+1/(2*3)+1/(3*4)+..+1/(99*100)