(20.24+12.24_48.22)÷82
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`(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
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
\(=\left(5\cdot2^6+11\cdot2^4-23\cdot2^4\right):2^6=5+11\cdot\dfrac{1}{2^2}-23\cdot\dfrac{1}{2^2}=5+\dfrac{11}{4}-\dfrac{23}{4}=2\)
\(A=4\left(\frac{1}{20}-\frac{1}{80}\right)=4.\frac{3}{80}=60\)
\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+\frac{16}{28\cdot32}+...+\frac{16}{76\cdot80}\)
\(A=4\left[\frac{4}{20\cdot24}+\frac{4}{24\cdot28}+\frac{4}{28\cdot32}+...+\frac{4}{76\cdot80}\right]\)
\(A=4\left[\frac{1}{20}-\frac{1}{24}+...+\frac{1}{76}-\frac{1}{80}\right]\)
\(A=4\left[\frac{1}{20}-\frac{1}{80}\right]\)
\(A=4\left[\frac{4}{80}-\frac{1}{80}\right]=4\cdot\frac{3}{80}=\frac{4\cdot3}{80}=\frac{1\cdot3}{20}=\frac{3}{20}\)
\(=4\left(\frac{4}{20.24}+\frac{4}{24.28}+...+\frac{4}{76.80}\right)\)
\(=4\left(\frac{1}{20}-\frac{1}{24}+\frac{1}{24}-\frac{1}{28}+...+\frac{1}{76}-\frac{1}{80}\right)\)
\(=4\left(\frac{1}{20}-\frac{1}{80}\right)\)
\(=4\times\frac{3}{80}\)
\(=\frac{12}{80}=\frac{3}{20}<1\)
đpcm
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
(20.24+12.24_48.22)÷82
=(20.16+12.16-48.4)÷64
={[16.(20+12)]-48.4}÷64
=(16.32-48.4)÷64
=(512-192)÷64=320÷64=5
(20.24+12.24_48.22)÷82
= (20.16 + 12.16-48.4):82
= 156: 82
=156:64
=2,4375