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a/b= (1+1/6) + (1/2+1/5) + (1/3+1/4)
a/b= 7/6 + 7/10 + 7/12
a/b= 7(1/6+1/10+1/12)
Vì 6x10x12 khong la boi so cua 7 => a/b chia het cho 7 <=> a chia het cho 7 (dpcm)
\(A=\frac{1}{3}.\frac{-9}{10}.\frac{-6}{13}.\frac{-13}{36}=\frac{-3}{10}.\frac{-1}{6}=\frac{1}{20}\)
\(B=\frac{4}{19}\left(\frac{-5}{12}+\frac{-7}{12}\right)-\frac{40}{57}=\frac{-4}{19}-\frac{40}{57}=\frac{-52}{57}\)
2 câu còn lại tự làm
\(A=\frac{1}{3}.\frac{-6}{13}.\frac{-9}{10}.\frac{-13}{36}\)
\(A=\frac{1}{1}.\frac{-2}{13}.\frac{-9}{10}.\frac{-13}{36}\)
\(A=\frac{-2}{13}.\frac{-9}{10}.\frac{-13}{36}\)
\(A=\frac{-1}{13}.\frac{-9}{5}.\frac{-13}{36}\)
\(A=\frac{-1}{13}.\frac{-1}{5}.\frac{-13}{4}\)
\(A=\frac{-13}{260}=\frac{-1}{20}\)
B=\(6\frac{4}{9}-4\frac{4}{9}+3\frac{7}{11}\)
B=\(2+3\frac{7}{11}\)
B=\(5\frac{7}{11}\)
B = \(5\frac{7}{11}=\frac{62}{11}\)
C = 1
D = \(\frac{5}{2}=2\frac{1}{2}\)
\(A=\frac{\frac{2}{3}+\frac{2}{5}-\frac{2}{9}}{\frac{4}{3}+\frac{4}{5}-\frac{4}{9}}\)
\(A=\frac{2.\frac{1}{3}+2.\frac{1}{5}-2.\frac{1}{9}}{4.\frac{1}{3}+4.\frac{1}{5}-4.\frac{1}{9}}\)
\(A=\frac{2.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}{4.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}\)
\(A=\frac{2}{4}=\frac{1}{2}\)
A =
2/3 + 2/5 - 2/9
___________
4/3 + 4/5 - 4/9
A =
2/3 + 2/5 -2/9
________________
2 . ( 2/3 + 2/5 - 2/9 )
=> A = 2
1/2+2/3+3/4+4/5+5/6+6/7+7/8+8/9+9/10x9/10
=9/10x(1/2+2/3)+(3/4+4/5)+(5/6+6/7)+(7/8+8/9)
=9/10x(1/3+3/5+5/7+7/9)
9/10x(1/3+3/5)+(5/7+7/9)
=9/10x1/5+5/9
9/50+5/9
=10
Bn Long làm đúng rồi bn 
nguyễn kim arica cứ làm theo cách đó là được .
Bn nào thấy đúng thì ủng hộ nha .
a ) \(\frac{5}{7}.\frac{-7}{9}-\frac{5}{7}.\frac{2}{9}-\frac{5}{9}\)
a, \(\frac{-3}{5}+\frac{7}{21}+\frac{-4}{5}+\frac{7}{5}\)
\(=\left(\frac{-3}{5}+\frac{-4}{5}+\frac{7}{5}\right)+\frac{7}{21}\)
\(=0+\frac{7}{21}\)
\(=\frac{7}{21}\)
\(=\frac{1}{3}\)
b, \(\frac{8}{9}+\frac{1}{9}.\frac{7}{9}+\frac{1}{9}.\frac{2}{9}\)
\(=\frac{8}{9}+\frac{1}{9}.\left(\frac{7}{9}+\frac{2}{9}\right)\)
\(=\frac{8}{9}+\frac{1}{9}.1\)
\(=\frac{8}{9}+\frac{1}{9}\)
\(=1\)
a) \(\frac{-3}{5}\)+\(\frac{7}{21}\)+\(\frac{-4}{5}\)+\(\frac{7}{5}\)
=(\(\frac{-3}{5}\)+\(\frac{-4}{5}\)+\(\frac{7}{5}\)) +\(\frac{7}{21}\)
= 0+
A=\(\frac{2\times\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}{4\times\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}=\frac{2}{4}=\frac{1}{2}\)
BẤM NÚT ĐÚNG HỘ MÌNH NHÉ
=1/2 nha bạn
tk và ủng hộ mk nha mk đang âm điểm