3/7 nha bạn

\(\frac{3}{10}\)+\(\frac{3}{40}\)+\(\frac{3}{88}\)+\(\frac{3}{154}\)

=\(\frac{3}{2.5}\)+\(\frac{3}{5.8}\)+\(\frac{3}{8.11}\)+\(\frac{3}{11.14}\)

Đến đây bạn tự suy luận tiếp nhé,mình không viết vào vì nó không cần thiết,phân tích xong nó sẽ như thế này:

=\(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}\)

Loại bỏ những phân số đối nhau ta còn:

=\(\frac{1}{2}-\frac{1}{14}\)

=\(\frac{7}{14}-\frac{1}{14}\)

=\(\frac{3}{7}\)

Chúc bạn học tốt^^

\(\frac{3}{10}+\frac{3}{40}+\frac{3}{88}+\frac{3}{154}\)

\(=\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}\)

\(=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}\)

\(=\frac{1}{2}-\frac{1}{14}\)

\(=\frac{3}{7}\)

(154-1)+1=154

154x155:2=11935

tick mk nha

1. 

$=153^2+2.47.153+47^2=(153+47)^2=200^2=40000$

2.

$=1,24^2-2.1,24.0,24+0,24^2=(1,24-0,24)^2=1^2=1$

3. Không phù hợp để tính nhanh 

4. 

$=15^8-(15^8-1)=1$

5.

$=(1^2-2^2)+(3^2-4^2)+(5^2-6^2)+...+(2019^2-2020^2)$

$=(1-2)(1+2)+(3-4)(3+4)+(5-6)(5+6)+...+(2019-2020)(2019+2020)$

$=(-1)(1+2)+(-1)(3+4)+(-1)(5+6)+....+(-1)(2019+2020)$

$=(-1)(1+2+3+4+....+2019+2020)=(-1).2020(2020+1):2=-2041210$

6:

\(\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)....\left(2^{2020}+1\right)+1\\ =1.\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)....\left(2^{2020}+1\right)+1\\ =\left(2-1\right)\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)....\left(2^{2020}+1\right)+1\\ =\left(2^2-1\right)\left(2^2+1\right)\left(2^4+1\right)....\left(2^{2020}+1\right)+1\\ =\left(2^4-1\right)\left(2^4+1\right)....\left(2^{2020}+1\right)+1\\ =\left(2^8-1\right)....\left(2^{2020}+1\right)+1\\ =\left(2^{2020}-1\right)\left(2^{2020}+1\right)+1\\ =2^{4040}-1+1=2^{4040}\)

Ta có: \(\left(2^{17}+15^4\right)\cdot\left(3^{19}-2^{17}\right)\cdot\left(2^4-4^2\right)\)

\(=\left(2^{17}+15^4\right)\left(3^{19}-2^{17}\right)\cdot\left(16-16\right)\)

=0

\(\frac{3}{10}+\frac{3}{40}+\frac{3}{88}+...+\frac{3}{460}\)

\(=\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+...+\frac{3}{20\cdot23}\)

\(=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{20}-\frac{1}{23}\)

\(=\frac{1}{2}-\frac{1}{23}\)

\(=\frac{21}{46}\)

Đáp án cần chọn là: A

Đáp án là A

Ta có (-154 + x) ⋮ 3

Mà -154 chia 3 dư 2. Vậy x chia 3 dư 1

5x84=420

12x35=420

7x22=154

11x14=154

2x77=154

5.x=420

x=420:5

x=84

12.x=420

x=420:12

x=35

7.x=154

x=154:7

x=22

11.x=154

x=154:11

x=14

2.x=154

x=154:2

x=77

5 x 84 = 420

12 x 35 = 420

7 x22 = 154

11 x 14 = 154 

2 x 77 = 154