`A = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + ... + 1/9900`
`A = 1/{1 × 2} + 1/{2 × 3} + 1/{3 × 4} + 1/{4 × 5} + 1/{5 × 6} + ... + 1/{99 × 100}`
`A = 1/1 × ( 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + ... + 1/99 - 1/100 )`
`A = 1/1 × ( 1/1 + 1/2 - 1/2 + 1/3 - 1/3 + 1/4 - 1/4 + 1/5 - 1/5 + 1/6 - 1/6 + ... + 1/99 - 1/99 - 1/100 )`
`A = 1/1 × ( 1/1 + 0 + 0 + 0 + 0 + 0 + ... + 0 - 1/100 )`
`A = 1/1 × ( 1/1 - 1/100 )`
`A = 1/1 × 99/100`
`A = 99/100`
`#dtkc`
