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2, tính vế trc
\(\frac{1}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+......+\frac{2}{19.21}\right)=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+.....+\frac{1}{19}-\frac{1}{21}\right)=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{21}\right)=\frac{1}{2}.\frac{2}{7}=\frac{1}{7}\)
=> 1/7 . x = 9/7
x = 9/7 . 7
x = 9
\(A=\frac{15\times3^{11}+4\times27^4}{9^7}\)
\(A=\frac{15\times177147+4\times531441}{4782969}\)
\(A=\frac{2657205+2125764}{4782969}\)
\(A=\frac{47829969}{47829969}=1\)
a) \(=\frac{6}{7}+\frac{5}{8}:5-\frac{3}{16}.4\)
\(=\frac{6}{7}+\frac{1}{8}-\frac{3}{4}\)
\(=\frac{13}{56}\)
b) \(=\frac{3}{2}+\frac{1}{2}.\frac{7}{18}:\frac{7}{12}\)
\(=\frac{3}{2}+\frac{1}{3}\)
\(=\frac{11}{6}\)
5) 327 - 48 - 152 + 173 =(327+173)-(48+152)=500-200=300
6) A = \(\frac{154+919+146+781}{823-217+533-139}=\frac{\left(154+146\right)+\left(919+781\right)}{1000}\)
=\(\frac{300+1700}{1000}=\frac{2000}{1000}=2\)
7) ( 1354 - 356 : 6 ) + 13,2=(1354\(-\frac{178}{3}\))+13,2=\(\frac{3884}{3}+13,2=\frac{19618}{15}\)
8) 784 . 0,5 : 0,28 - 196 : 28 + 2003=392:0,28-7+2003
=1400-7+2003=3396