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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
\(=\left(5\cdot2^6+11\cdot2^4-23\cdot2^4\right):2^6=5+11\cdot\dfrac{1}{2^2}-23\cdot\dfrac{1}{2^2}=5+\dfrac{11}{4}-\dfrac{23}{4}=2\)
99 x 82 + 99 x 12 + 12 x 99 + 12 x 82
= 99 x 82 + 12 x 82
= ( 99 + 12 ) x 82
=111 x 82
= kiểu vậy đúng ko mấy chế sợ sai lắm
\(49(82+18)+100+50(89+11)\)
\(=49\cdot100+100+50\cdot100\)
\(=100\left(49+50+1\right)\)
\(=100\cdot100=10000\)
49 . (82 + 18) + 100 + 50 . (89 + 11)
= 49 . 100 + 100 + 50 . 100
= 100.(49 + 1 + 50)
= 100 . 100
= 10000
22344.18.2+24668.41.2
=402192.2+1011388.2
=2.(402192+1011388)
=2.1413580
=2827160
\(A=4\left(\frac{1}{20}-\frac{1}{80}\right)=4.\frac{3}{80}=60\)
\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+\frac{16}{28\cdot32}+...+\frac{16}{76\cdot80}\)
\(A=4\left[\frac{4}{20\cdot24}+\frac{4}{24\cdot28}+\frac{4}{28\cdot32}+...+\frac{4}{76\cdot80}\right]\)
\(A=4\left[\frac{1}{20}-\frac{1}{24}+...+\frac{1}{76}-\frac{1}{80}\right]\)
\(A=4\left[\frac{1}{20}-\frac{1}{80}\right]\)
\(A=4\left[\frac{4}{80}-\frac{1}{80}\right]=4\cdot\frac{3}{80}=\frac{4\cdot3}{80}=\frac{1\cdot3}{20}=\frac{3}{20}\)
`(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