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a: \(2,5:4x=0,5:0,2\)
=>\(2,5:4x=0,5\cdot5=2,5\)
=>4x=1
=>\(x=\dfrac{1}{4}\)
b: \(3,8:2x=\dfrac{1}{4}:2\dfrac{2}{3}\)
=>\(3,8:2x=\dfrac{1}{4}:\dfrac{8}{3}=\dfrac{1}{4}\cdot\dfrac{3}{8}=\dfrac{3}{32}\)
=>\(2x=3,8:\dfrac{3}{32}=\dfrac{19}{5}\cdot\dfrac{32}{3}=\dfrac{608}{15}\)
=>\(x=\dfrac{608}{15}:2=\dfrac{304}{15}\)
c: \(5,25:7x=3,6:2,4\)
=>\(5,25:7x=1,5\)
=>\(7x=5,25:1,5=3,5\)
=>\(x=\dfrac{3.5}{7}=0,5\)
d: \(1,8:1,3=-2,7:5x\)
=>\(5x=-2,7:\dfrac{18}{13}=-2,7\cdot\dfrac{13}{18}=-1,95\)
=>\(x=-1,95:5=-0,39\)
Bài 1:
b) Ta có: \(D=\dfrac{-5}{10}\cdot\dfrac{-4}{10}\cdot\dfrac{-3}{10}\cdot...\cdot\dfrac{3}{10}\cdot\dfrac{4}{10}\cdot\dfrac{5}{10}\)
\(=\dfrac{-5}{10}\cdot\dfrac{-4}{10}\cdot\dfrac{-3}{10}\cdot...\cdot0\cdot...\cdot\dfrac{3}{10}\cdot\dfrac{4}{10}\cdot\dfrac{5}{10}\)
=0
ii: Ta có: 15:4=x:3.5
nên \(x=\dfrac{3.5\cdot15}{4}=\dfrac{105}{8}\)
\(\frac{2x-10}{6}=\frac{-27}{5-x}\)
\(\frac{2\left(x-5\right)}{6}=\frac{27}{x-5}\)
\(2\left(x-5\right)^2=27\times6\)
\(2x^2-20x+50-162=0\)
\(2x^2-20x-112=0\)
\(x^2-10x-56=0\)
\(x^2-14x+4x-56=0\)
\(\left(x-14\right)\left(x+4\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-14=0\\x+4=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=14\\x=-4\end{cases}}\)
KL .....
XIN TIICK
a, 7,2 +(-2,7) + 1,8 - 0,3
= (7,2 + 1,8) - (2,7 + 0,3)
=9 - 3
= 6
b, \(\dfrac{32}{5}\) + 11,5 - 6,7 + (2,4) - \(\dfrac{10}{4}\) + \(\dfrac{27}{10}\)
= 6,4 + 11,5 - 6,7 + 2,4 - 2,5 + 2,7
= (6,4 + 2,4) + ( 11,5 - 2,5) - (6,7 - 2,7)
= 8,8 + 9 - 4
= 8,8 + 5
= 13,8
tính nhanh nha