`(20.2^4+12.2^4-48.2^2):8^2`

`=(32.2^4-12.2^4):8^2`

`=[2^4.(32-12)]:8^2`

`=20.2^4:8^2`

`=20.16:64`

`=5`

Ta có: \(\left(20\cdot2^4+12\cdot2^4-48\cdot2^2\right):8^2\)

\(=\left(32\cdot2^4-12\cdot2^4\right):2^6\)

\(=20\cdot\dfrac{2^4}{2^6}\)

=5

12=6x6

24=????

chịu bạn

A=1.5+2.6+3.7+...+20.24

A=1.(2+3) + 2.(3+3) + 3.(4+3) + ... + 20.(21+3)

A=1.2+3 + 2.3 +6 + 3.4 +9 + ... + 20.21 + 60

A= (1.2+2.3+3.4+...+20.21) + (3+6+9+...+60)

Tính B= 1.2 + 2.3 + 3.4 +...+ 20.21

3.B= 1.2.3 + 2.3.3 + 3.4.3 +...+ 20.21.3

3B= 1.2.3 + 2.3.(4-1) + 3.4. (5-2) + ... + 20.21. (22-19)

3B= 20.21.22 suy ra B= 3080

Tính 3+6+9+...+60= [(60-3):3+1](3+60):2=630

Vậy A= 3080 + 630=3710

\(\left(20.2^4+11.2^4-23.2^4\right):2^6\)

\(=\left[2^4.\left(20+11-23\right)\right]:2^6\)

\(=\left(2^4.8\right):2^6\)

\(=2^4.2^3:2^6\)

\(=2\)

\(\left(20.2^4+11.2^4-32.2^4\right):6=\left[2^4\left(20+11-32\right)\right]:6=\)

\(=\left[2^4.1\right]:2^6=2^2\)

\(=\left(5\cdot2^6+11\cdot2^4-23\cdot2^4\right):2^6=5+11\cdot\dfrac{1}{2^2}-23\cdot\dfrac{1}{2^2}=5+\dfrac{11}{4}-\dfrac{23}{4}=2\)

\(A=4\left(\frac{1}{20}-\frac{1}{80}\right)=4.\frac{3}{80}=60\)

\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+\frac{16}{28\cdot32}+...+\frac{16}{76\cdot80}\)

\(A=4\left[\frac{4}{20\cdot24}+\frac{4}{24\cdot28}+\frac{4}{28\cdot32}+...+\frac{4}{76\cdot80}\right]\)

\(A=4\left[\frac{1}{20}-\frac{1}{24}+...+\frac{1}{76}-\frac{1}{80}\right]\)

\(A=4\left[\frac{1}{20}-\frac{1}{80}\right]\)

\(A=4\left[\frac{4}{80}-\frac{1}{80}\right]=4\cdot\frac{3}{80}=\frac{4\cdot3}{80}=\frac{1\cdot3}{20}=\frac{3}{20}\)

\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+...+\frac{16}{76\cdot80}\)

\(A=\frac{4^2}{\left(5\cdot6\right)\cdot4^2}+\frac{4^2}{\left(6\cdot7\right)\cdot4^2}+...+\frac{4^2}{\left(19\cdot20\right)\cdot4^2}\)

\(A=\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{19\cdot20}\)

\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{19}-\frac{1}{20}=\frac{1}{5}-\frac{1}{20}=\frac{3}{20}\)

wkwkwkwkwkwk

\(=4\left(\frac{4}{20.24}+\frac{4}{24.28}+...+\frac{4}{76.80}\right)\)

\(=4\left(\frac{1}{20}-\frac{1}{24}+\frac{1}{24}-\frac{1}{28}+...+\frac{1}{76}-\frac{1}{80}\right)\)

\(=4\left(\frac{1}{20}-\frac{1}{80}\right)\)

\(=4\times\frac{3}{80}\)

\(=\frac{12}{80}=\frac{3}{20}<1\)

đpcm

frtji

1)

2/3.5+2/5.7+...+2/11.13+2/13.15+2/1.2+2/2.3+...+2/9.10

=(2/3.5+...2/13.15)+(2/1.2+...+2/9.10)

= (2/3-2/15)+ [2(1-1/10)]

=8/15+9/5

=7/3

2)

11/12+11/12.24+...+11/88.99

=11-1/9

=10/8/9