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a: \(\Leftrightarrow\dfrac{16}{x}=\dfrac{-4}{5}\)
hay x=-20
b: =>x+7=-10
hay x=-17
\(B=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}\)
=>\(B=\dfrac{32}{64}+\dfrac{16}{64}+\dfrac{6}{64}+\dfrac{2}{64}+\dfrac{1}{64}\)
=>\(B=\dfrac{32+16+6+2+1}{64}\)
=>\(B=\dfrac{63}{64}\)
M = 1/21 + 1/28+1/36+...+1/465
= 2/42+2/56+2/72+...+2/930
= 2.( 1/6.7 + 1/7.8 + 1/ 7.9 + ... + 1/30.31)
= 2.( 1/6-1/7+1/7-1/8+...+1/30-1/31)
= 2.(1/6 - 1/31) = 2.25/186 = 25/92
\(12.\left(\dfrac{29292929}{56565656}+\dfrac{66666}{77777}\right)=12.\left(\dfrac{29}{56}+\dfrac{6}{7}\right)=12.\left(\dfrac{29}{56}+\dfrac{48}{56}\right)=12.\dfrac{77}{56}=\dfrac{33}{2}\)
\(12.\left(\dfrac{29292929}{56565656}+\dfrac{66666}{77777}\right)=12.\left(\dfrac{29.1010101}{56.1010101}+\dfrac{6.11111}{7.11111}\right)=12.\left(\dfrac{29}{56}+\dfrac{6}{7}\right)=12.\dfrac{11}{8}=\dfrac{33}{2}\)
\(x=\dfrac{5}{8}+\dfrac{1}{8}\)
\(x=\dfrac{6}{8}=\dfrac{3}{4}\)
\(x=\dfrac{4}{27}-\dfrac{2}{3}\)
\(x=-\dfrac{14}{27}\)
\(x=\dfrac{35.16}{-28}\)
\(x=-20\)
\(\dfrac{-28}{35}=\dfrac{16}{x}\\ \Rightarrow-28\cdot x=35\cdot16=560\\ x=560:-28\\ x=-20\)