Mn giúp mình với nha

Đáp án:

Giải thích các bước giải:

 `a) → x- 10. (2/(11. 13)+ 2/(13. 15)+ 2/(15. 17)+....+ 2/(53. 55))= 3/11`

`→ x- 10. (1/11- 1/13+ 1/13- 1/15+ 1/15- 1/17+...1/53- 1/55)= 3/11`

`→x- 10. (1/11- 1/55)= 3/11`

`→ x- 10. 4/55= 3/11`

`x- 8/11= 3/11`

`x= 3/11+ 8/11`

`→ x= 1`

`b)` trong ảnh

`c) → 2/3x- 780/11: (13/15+ 13/35+ 13/63+13/99)= -5`

`→2/3x- 780/11: 13 (1/5+ 1/35+ 1/63+ 1/99)= -5`

`→ 2/3x- 780/11: 13 4/33= -5`

`→ 2/3x- 780/11: 52/33= -5`

`→ 2/3x- 45= -5`

`→ 2/3x= -5+ 45`

`→ 2/3x= 40`

`x= 40: 2/3`

`x= 40. 3/2`

`x= 60`

`d)  A = 1/100. (100/(1. 101)+ 100/(2. 102)+ 100/ (3. 103)+...+ 100.(10. 110))`

`A = 1/100. (1- 1/101+ 1/2- 102+...+ 1/10- 1/110)`

`A = 1/100. (1+ 1/2+...+ 1/10)- (1/101+ 1/102+...+ 1/110))`

`B = 1/(1. 11)+ 1/(2. 102)+...+ 1/(100. 110)`

`B= 1/10. (10/(1. 11)+ 10/(2. 12)+...+ 10/(100. 110))`

`B= 1/10. (1- 1/11+ 1/2- 1/2+...+ 1/100- 1/110)`

`B= 1/10. (1+ 1/2+...+ 1/100)- (1/11+ 1/12+...+ 1/110)= 1/10. (1+ 1/2+...+ 1/10)- (1/101+ 1/102+...+ 1/110))`

`B= 10A`

`A.x= 10A`

`→ x= 10`

`B=