`9. A = -( 1/2 . 2/3 . 3/4 .... 9/10)`
`A = -( 1/10 )`
`A = -1/10`
`10. A= ( 1/2 + 1 ) ( 1/2 - 1) . ( 1/3 - 1 ) ( 1/3 + 1 ) ....( 1/99 + 1 ) ( 1/99 + 1 ). ( 1/100 + 1 ) ( 1/100 - 1 )`
`= 3/2 . -1/2 . -2/3 . 4/3 ... 100/99 . 98/100 . -99/100 . 101/100`
`= 1/2 .101/100`
`= 101/200`
`11. `
`B = ( 1/2^2 - 1 ) ( 1/3^2 - 1 ) ...( 1/10^2 - 1) `
`= - ( 3/2^2 . 8/3^2 ... 99/10^2 )`
`= -( (1.3)/(2.2) . ( 2.4)/(3.3) ... (9.11)/(10.10)`
`= - ( (1.2.3...9)/(2.3.4...10) . ( 3.4.5..11)/(2.3.4...10))`
`= -(1/10 . 11/2 )`
`= -11/20 < -11/21`
