Tìm x biết: 1/ 1 x2 + 1/ 2x3 + 1/ 3x4 + ... + 1/ x x ( x+1 ) = 30/31 .
Giải thích
11×2+12×3+13×4+...+1x×(x+1)=30311−12+12−13+14−14+...+1x−1x+1=3031 1−1x+1=3031 xx+1=3031
Vậy x = 30
11×2+12×3+13×4+...+1x×(x+1)=30311−12+12−13+14−14+...+1x−1x+1=3031 1−1x+1=3031 xx+1=3031
Vậy x = 30