Cao nhân nào cứu em một mạng vớiii

Bài 2:

`a)`

`(4 5/37 - 3 4/5 + 8 15/29) - (3 5/37 - 6 14/29)`

`= 4 + 5/37 - 3 - 4/5 + 8 + 15/29 - 3 - 5/37 + 6 + 14/29`

`= (4 - 3 + 8 - 3 + 6) + (5/37 - 5/37) + (15/29 + 14/29) - 4/5`

`= 12 + 0 + 29/29 - 4/5`

`= 12 + 1 - 4/5`

`= 13 - 4/5`

`= 61/5`

`b)`

`7/(-25) + (-18)/25 + 4/23 + 5/7 + 19/23`

`= -7/25 - 18/25 + 4/23 + 5/7 + 19/23`

`= (-7/25 - 18/25) + (4/23 + 19/23) + 5/7`

`= -1 + 1 + 5/7`

`= 0 + 5/7`

`= 5/7`

`c)`

`(-5)/17 * (-9)/23 + (-9)/23 * 22/17`

`= (-9)/23 * ((-5)/17 + 22/17)`

`= (-9)/23 * 1`

`= -9/23`

`d)`

`(-7)/19 * 8/11 + (-7)/19 * 3/11 - 12/19`

`= (-7)/19 * (8/11 + 3/11) - 12/19`

` = (-7)/19 * 1 - 12/19`

`= -7/19 - 12/19`

`= -1`

``

Bài 3:

`a)`

`A = 2/(3*5) + 2/(5*7) + 2/(7*9) + ... + 2/(61*63)`

`A = (1/3 - 1/5) + (1/5 - 1/7) + (1/7 - 1/9) + ... + (1/61 - 1/63)`

`A = 1/3 - 1/63`

`A = 20/63`

`b)`

`B = 2/(1*4) + 2/(4*7) + 2/(7*10) + ... + 2/(100*103)`

`B = 2/3 * (3/(1*4) + 3/(4*7) + 3/(7*10) + ... + 3/(100*103))`

`B = 2/3 * ((1/1 - 1/4) + (1/4 - 1/7) + (1/7 - 1/10) + ... + (1/100 - 1/103))`

`B = 2/3 * (1 - 1/103)`

`B = 2/3 * (102/103)`

`B = 68/103`

`c)`

`C = 10/56 + 10/140 + 10/260 + ... + 10/1400`

` C = 10/(2*28) + 10/(2*70) + 10/(2*130) + ... + 10/(2*700)`

`C = 5/28 + 5/70 + 5/130 + ... + 5/700`

`C = 5/(4*7) + 5/(7*10) + 5/(10*13) + ... + 5/(25*28) `

`C = 5/3 * [ 3/(4*7) + 3/(7*10) + 3/(10*13) + ... + 3/(25*28) ]`

`C = 5/3 * [ (1/4 - 1/7) + (1/7 - 1/10) + (1/10 - 1/13) + ... + (1/25 - 1/28) ] `

`C = 5/3 * [ 1/4 - 1/28 ]`

`C = 5 / 14`