tinh nhanh
A = 55/11x16 + 55/16x21 + 55/21x26 + 55/26x31 + 55/31x36 + 55/36x41
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NH
1
11 tháng 6 2015
Ta có:
55/11x16+55/16x21+55/21x26x.....x55/36x41
=55/5 x (1/11-1/16+1/16-1/21+.......+1/36-1/41)
=55/5 x (1/11-1/41)
=55/5x30/451
=30/41
nhớ ****
7 tháng 5 2022
`A = 55/( 11xx16 ) + 55/( 16xx21 ) + 55/( 21xx26 ) + 55/( 26xx31) + 55/( 31xx36)+55/(36xx41)`
`A = 11 xx ( 5/( 11xx16 ) + 5/( 16xx21 ) + 5/( 21xx26 ) + 5/( 26xx31) + 5/( 31xx36)+5/(36xx41)`
`A = 11 xx ( 1/11 - 1/16 + 1/16 - 1/21 + 1/21 - 1/26 + 1/26 - 1/31 + 1/31 - 1/36 + 1/36 - 1/41 )`
`A = 11 xx ( 1/11 - 1/41 )`
`A = 1 - 11/41`
`A = 30/41`
TC
7 tháng 5 2022
\(A=55.\left(\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{21}+\dfrac{1}{21}-\dfrac{1}{26}+\dfrac{1}{26}-\dfrac{1}{31}+\dfrac{1}{31}-\dfrac{1}{36}+\dfrac{1}{36}-\dfrac{1}{41}\right)\)
\(A=55\times\left(\dfrac{1}{11}-\dfrac{1}{41}\right)=55\times\dfrac{30}{451}=\dfrac{150}{41}\)
LQ
1
HN
3
DP
25 tháng 3 2017
\(\frac{55}{11\times6}+\frac{55}{16\times21}+\frac{55}{21\times26}+..+\frac{55}{36\times41}\)
\(=\frac{11-6}{11\times6}+\frac{21-16}{16\times21}+..+\frac{41-36}{36\times41}\)
\(=1-\frac{1}{11}+\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+..+\frac{1}{36}-\frac{1}{41}\)
\(=1-\frac{1}{41}\)
\(=\frac{40}{41}\)
5 tháng 6 2017
\(A=\frac{55}{11.16}+\frac{55}{16.21}+\frac{55}{21.26}+......+\frac{55}{36.41}\)
\(=11\left(\frac{5}{11.16}+\frac{5}{16.21}+......+\frac{5}{36.41}\right)\)
\(=11.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+.......+\frac{1}{36}-\frac{1}{41}\right)\)
\(=11.\left(\frac{1}{11}-\frac{1}{41}\right)\)
\(=11.\frac{30}{451}=\frac{30}{41}\)
TM
29 tháng 7 2017
\(A=\frac{55}{11x16}+\frac{55}{16x21}+\frac{55}{21x26}+\frac{55}{26x31}+\frac{55}{31x36}+\frac{55}{36x41}\)
\(A=11\left(\frac{5}{11x16}+\frac{5}{16x21}+\frac{5}{21x26}+\frac{5}{26x31}+\frac{5}{31x36}+\frac{5}{36x41}\right)\)
\(A=11\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+\frac{1}{26}-\frac{1}{31}+\frac{1}{31}-\frac{1}{36}+\frac{1}{36}-\frac{1}{41}\right)\)
\(A=11\left(\frac{1}{11}-\frac{1}{41}\right)=1-\frac{11}{41}=\frac{30}{41}\)
HT
14 tháng 7 2015
\(\frac{55}{16.21}\)chứ nhỉ.
A=\(\frac{55}{11.16}+\frac{55}{16.21}+\frac{55}{21.26}+\frac{55}{26.31}+\frac{55}{31.36}+\frac{55}{36.41}\)
A= 11.\(\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+....+\frac{1}{36}-\frac{1}{41}\right)\)
A= 11\(\left(\frac{1}{11}-\frac{1}{41}\right)\)
A= 11.\(\frac{30}{451}\)
A= \(\frac{30}{41}\)
19 tháng 7 2016
\(A=11\left(\frac{5}{11.6}+\frac{5}{16.21}+......+\frac{5}{36.41}\right)\)
\(=11\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+.....+\frac{1}{36}-\frac{1}{41}\right)\)
\(=11\left(\frac{1}{11}-\frac{1}{41}\right)\)
\(=11.\frac{30}{451}=\frac{30}{41}\)
NT
1
26 tháng 7 2023
\(=11\left(\dfrac{5}{6\cdot11}+\dfrac{5}{11\cdot16}+\dfrac{5}{16\cdot21}+\dfrac{5}{21\cdot26}+\dfrac{5}{26\cdot31}\right)\)
=11(1/6-1/11+1/11-1/16+1/16-1/21+1/21-1/26+1/26-1/31)
=11*25/186=275/186
\(\frac{A}{11}=\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+\frac{5}{26.31}+\frac{5}{31.36}+\frac{5}{36.41}\)
\(\frac{A}{11}=\frac{16-11}{11.16}+\frac{21-16}{16.21}+\frac{26-21}{21.26}+...+\frac{41-36}{36.41}\)
\(\frac{A}{11}=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{36}-\frac{1}{41}\)
\(\frac{A}{11}=\frac{1}{11}-\frac{1}{41}=\frac{30}{11.41}\Rightarrow A=\frac{11.30}{11.41}=\frac{30}{41}\)
\(\sqrt[1]{\dfrac{2}{3}_3\dfrac{1}{2}3_3\dfrac{3}{4}^3}\)