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\(A=\frac{3}{4}.\frac{8}{9}.\frac{15}{16}......\frac{889}{900}\)
\(=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}.....\frac{29\cdot31}{30.30}\)
\(=\frac{1.3.2.4.3.5.....29.31}{2.2.3.3.4.4....30.30}\)
\(=\frac{\left(1.2.3....29\right)\left(3.4.5...31\right)}{\left(2.3.4....30\right)\left(2.3.4.....30\right)}\)
\(=\frac{1.31}{30.2}=\frac{31}{60}\)
\(1\frac{1}{2}.1\frac{1}{3}.1\frac{1}{4}.....1\frac{1}{2015}\)
\(=\frac{3}{2}.\frac{4}{3}.\frac{5}{4}........\frac{2016}{2015}\)
\(=\frac{3.4.5.....2016}{2.3.4....2015}=\frac{2016}{2}=1008\)
\(A=\frac{3}{2}.\frac{4}{3}.\frac{5}{4}...\frac{2016}{2015}\)
\(A=\frac{2016}{2}=1008\)
Xong nhé bạn!
1,2 . \(\left[\frac{2,4x-0,23}{x}-0,05\right]=1,44\)
\(\left[\frac{2,4x-0,23}{x}-0,05\right]=1,2\)
\(\frac{2,4x-0,23}{x}=1,25\)
Làm tiếp nha
Ta có :
\(\frac{23+a}{40+a}=\frac{3}{4}\)
=> 4 ( 23 + a ) = 3 ( 40 + a )
=> 92 + 4a = 120 + 3a
=> 4a - 3a = 120 - 92
=> a = 28
\(\frac{11}{2}-2,4< a< 1,35:0,15\)
=> 3,1 < a < 9
MÀ a thuộc N
=> a \(\in\){ 4 ; 5 ; 6 ; 7 ; 8 }
Vậy a \(\in\){ 4 ; 5 ; 6 ; 7 ; 8 }
Ta có :
11/2 - 12/5 < a < 27/20 . 20/3
3,1 < a < 9
Vì a thuộc N nên :
---> a thuộc { 4 ; 5 ; 6 ; 7 ; 8 }
sửa câu a
\(5,2.x+7\frac{2}{5}=6\frac{3}{4}=>\frac{26}{5}.x+\frac{37}{5}=\frac{27}{4}=>\frac{26}{5}.x=\frac{27}{4}-\frac{37}{5}\)
\(\frac{26}{5}.x=-\frac{13}{20}=>x=-\frac{13}{20}:\frac{26}{5}=>x=-\frac{1}{8}\)
vậy \(x=-\frac{1}{8}\)
a) \(5,2\cdot x+7\frac{2}{5}=6\frac{3}{4}\)
=> \(5,2\cdot x=6\frac{3}{4}-7\frac{2}{5}=\frac{27}{4}-\frac{37}{5}=-\frac{13}{20}\)
=> \(x=-\frac{13}{20}:5,2=-\frac{13}{20}:\frac{26}{5}=-\frac{13}{20}\cdot\frac{5}{26}=-\frac{1}{8}\)
b) \(2,4:\left(\frac{-1}{2}-x\right)=1\frac{3}{5}\)
=> \(\frac{-1}{2}-x=2,4:1\frac{3}{5}=\frac{12}{5}:\frac{8}{5}=\frac{12}{5}\cdot\frac{5}{8}=\frac{3}{2}\)
=> \(x=-\frac{1}{2}-\frac{3}{2}=-\frac{4}{2}=-2\)
1035 nhe