Question

得出规律并计算二分之一加六分之一加十二分之一加二十分之一家三十分之一加四十分之一加五十六分之一加七十二分之一加九十

Answer 1

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90

=1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)+1/(9×10)

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10

=1-1/10

=9/10