Câu 1:A= $\dfrac{1}{3x4}$+$\dfrac{1}{4x5}$+$\dfrac{1}{5x6}$+....+$\dfrac{1}{98x99}$
Câu 2:B= $\dfrac{1}{5x6}$+$\dfrac{1}{6x7}$+$\dfrac{1}{7x8}$+....+$\dfrac{1}

Question

Câu 1:A= $\dfrac{1}{3x4}$+$\dfrac{1}{4x5}$+$\dfrac{1}{5x6}$+....+$\dfrac{1}{98x99}$
Câu 2:B= $\dfrac{1}{5x6}$+$\dfrac{1}{6x7}$+$\dfrac{1}{7x8}$+....+$\dfrac{1}{34x35}$
Câu 3:C= $\dfrac{1}{1x3}$+$\dfrac{1}{3x5}$+$\dfrac{1}{5x7}$+....+$\dfrac{1}{99x101}$
Câu 4:D= $\dfrac{1}{2x4}$+$\dfrac{1}{4x6}$+$\dfrac{1}{6x8}$+....+$\dfrac{1}{48x50}$
Câu 5:M= $\dfrac{1}{2x5}$+$\dfrac{1}{5x8}$+$\dfrac{1}{8x11}$+....+$\dfrac{1}{1979x1982}$
Câu 6:N= $\dfrac{1}{1x3}$+$\dfrac{1}{3x5}$+$\dfrac{1}{5x7}$+....+$\dfrac{1}{97x99}$

maivu21 · Answer

Câu `1:`
`A=1/3.4+1/4.5+1/5.6+...+1/98.99`
`A=1/3-1/4+1/4-1/5+...+1/98-1/99`
`A=1/3-1/99`
`A=32/99`
 Vậy `A=32/99`
````
Câu `2:`
`B=1/5.6+1/6.7+1/7.8+...+1/34.35`
`B=1/5-1/6+1/6-1/7+1/7-1/8+...+1/34-1/35`
`B=1/5-1/35`
`B=6/35`
 Vậy `B=6/35`
````
Câu `3:`
`C=1/1.3+1/3.5+1/5.7+...+1/99.101`
`2C=2.(1/1.3+1/3.5+1/5.7+...+1/99.101)`
`2C=2/1.3+2/3.5+2/5.7+...+2/99.101`
`2C=1-1/3+1/3-1/5+...+1/99-1/101`
`2C=1-1/101`
`2C=100/101`
`C=100/101 :2`
`C=100/101 . 1/2`
`C=50/101`
 Vậy `C=50/101`
````
Câu `4:`
`D=1/2.4+1/4.6+1/6.8+...+1/48.50`
`2D=2.(1/2.4+1/4.6+1/6.8+...+1/48.50)`
`2D=2/2.4+2/4.6+2/6.8+...+2/48.50`
`2D=1/2-1/4+1/4-1/6+1/6-1/8+...+1/48-1/50`
`2D=1/2-1/50`
`2D=12/25`
`D=12/25 :2`
`D=12/25 .1/2`
`D=6/25`
 Vậy `D=6/25`
````
Câu `5:`
`M=1/2.5+1/5.8+1/8.11+...+1/1979.1982`
`3M=3.(1/2.5+1/5.8+1/8.11+...+1/1979.1982)`
`3M=3/2.5+3/5.8+3/8.11+...+3/1979.1982`
`3M=1/2-1/5+1/5-1/8+...+1/1979-1/1982`
`3M=1/2-1/1982`
`3M=495/991`
`M=495/991 :3`
`M=495/991 .1/3`
`M=165/991`
 Vậy `M=165/991`
````
Câu `6:`
`N=1/1.3+1/3.5+1/5.7+...+1/97.99`
`2N=2.(1/1.3+1/3.5+1/5.7+...+1/97.99)`
`2N=2/1.3+2/3.5+2/5.7+...+2/97.99`
`2N=1-1/3+1/3-1/5+...+1/97-1/99`
`2N=1-1/99`
`2N=98/99`
`N=98/99 :2`
`N=98/99 .1/2`
`N=49/99`
 Vậy `N=49/99`

nguyenhongphuonguyen · Answer

Đáp án:
 
Giải thích các bước giải:
 `1)``A = 1/3.4 + 1/4.5 + 1/5.6 +... + 1/98.99`
`A =1/3 - 1/4 + 1/4 - 1/5 +1/5 - 1/6 +.... + 1/98 - 1/99`
`A = 1/3 - 1/99`
`A = 32/99`
Vậy `A = 32/99`
`2)B = 1/5.6 + 1/6.7 + 1/7.8 +... + 1/34.35`
`B = 1/5 - 1/6 + 1/6 - 1/7  +1/7 - 1/8 +... + 1/34 - 1/35`
`B= 1/5 - 1/35`
`B = 7/35 - 1/35`
`B = 6/35`
Vậy `B = 6/35`
`3) C = 1/1.3 + 1/3.5 + 1/5.7 +... + 1/99.101`
`C = 1/2(2/1.3 + 2/3.5 + 2/5.7 +... + 2/99.101)`
`C = 1/2 ( 1/1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 +... + 1/99 - 1/101)`
`C = 1/2 ( 1/1 - 1/101)`
`C = 1/2 - 1/202`
`C = 50/101`
Vậy `C = 50/101`
`4) D = 1/2.4 + 1/4.6  +1/6.8 +... + 1/48.50`
`D = 1/2(2/2.4 + 2/4.6 + 2/6.8 +... + 2/48.50)`
`D = 1/2(1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 +... + 1/348  -1/50)`
`D = 1/2(1/2 - 1/50)`
`D = 1/2 . 12/25`
`D = 6/25`
Vậy `D = 6/25`
`5) M = 1/2.5 + 1/5.8 + 1/8.11 +... + 1/1979.1982`
`M = 1/3(3/2.5 + 3/5.8 + 3/8.11+... + 3/1979.1982)`
`M = 1/2(1/2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/11 +.... + 1/1979 - 1/1982)`
`M = 1/2(1/2 - 1/1982)`
`M = 1/2 . 495/991`
`M = 495/1982`
Vậy `M = 495/1982`
`6) N = 1/1.3 + 1/3.5 + 1/5.7 +... + 1/97.99)`
`N = 1/2(2/1.3 + 2/3.5 + 2/5.7 +... + 2/97.99)`
`N = 1/2(1/1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 +.... + 1/97 -1/99)`
`N = 1/2(1/1 - 1/99)`
`N = 1/2 . 98/99`
`N = 49/99`
Vậy `N = 49/99`

TRẢ LỜI

Bạn muốn hỏi điều gì?

Tham Gia Group Dành Cho Lớp 6 Chia Sẻ, Trao Đổi Tài Liệu Miễn Phí

Bạn muốn hỏi điều gì?

Tìm kiếm với hình ảnh

Hãy đăng nhập hoặc tạo tài khoản miễn phí!

Lưu vào

TRẢ LỜI

Bạn muốn hỏi điều gì?

Tham Gia Group Dành Cho Lớp 6 Chia Sẻ, Trao Đổi Tài Liệu Miễn Phí

Bạn muốn hỏi điều gì?

Lý do báo cáo vi phạm?