1）1x2+2x3+3x4+...+100x101

1）1x2+2x3+3x4+...+100x101= 2）1x2+2x3+3x4+...n(n+1)= （3）1x2x3

2个回答

(1)1x2+2x3+3x4+...+100x101=1/3*(100*101*102-99*100*101+99*100*101.-0*1*2)=1/3*102*100*101=343400(2)1x2+2x3+3x4+...n(n+1)==1/3*[n*(n+1)*(n+2)-(n-1)*n*(n+1).-0*1*2]=1/3n(n+1)(n+2)(3)1x2x3+2x3x4+3x4x5+.....

1X2X3+2X3X4+.+n(n+1)(n+2)
1x2x3+2x3x4+.+n(n+1)(n+2)=?
有趣的数学题1.1x2x3 + 2x3x4 + 3x4x5 +.+100x101x102 2.1/(1x2x3) + 1
1x2x3+2x3x4+.+nx(n+1)(n+2)=?
Sn=1/(1x2x3)+1/(2x3x4)+...+1/(n(n+1)(n+2))
1x(乘号）2+2x3+3x4+.+100x101=?
1x1-2x2+3x3-4x4+5x5-6x6.-100x100+101x101
求 4/(x+1)(x+3) + 4/(x+3)(x+5) +.+ 4/(x+2n-1)(x+2n+1)
：（X1+X2+X3）~N（0,3）,：（X4+X5+X6）~N（0,3）,所以 (1/3)*[（X1+X2+X3)^2
已知f(x)=1+x-x^2/2+x^3-x^4/4+.x^101/101 ,g(x)=1-x+x^2/2-x^3/3.