Question

[Pham Thi Gia Hy]

\(\frac{8}{9}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)

Answer 1

[soyeon_Tiểu bàng giải]

8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2

= 8/9 - (1/2 + 1/6 + 1/12 + ... + 1/72)

= 8/9 - (1/1×2 + 1/2×3 + 1/3×4 + ... + 1/8×9)

= 8/9 - (1 - 1/2 + 1/2 - 1/3 × 1/3 - 1/4 + ... + 1/8 - 1/9)

= 8/9 - (1 - 1/9)

= 8/9 - 8/9

= 0

^_^◆_◆☆_★^_-

Answer 2

[Sherlockichi Kudoyle]

\(=\frac{8}{9}-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\right)\)

\(=\frac{8}{9}-\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)\)

\(=\frac{8}{9}-\left(\frac{1}{1}-\frac{1}{9}\right)\)

\(=\frac{8}{9}-\frac{8}{9}=0\)