Tìm x :
4/7+x=5/7x1/2
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\(=\dfrac{3}{7}\times\left(\dfrac{1}{5}+\dfrac{2}{3}-\dfrac{1}{8}\right)\\ =\dfrac{3}{7}\times\left(\dfrac{24}{5\times24}+\dfrac{2\times40}{3\times40}-\dfrac{15}{8\times15}\right)\\ =\dfrac{3}{7}\times\left(\dfrac{24+80-15}{120}\right)\\ =\dfrac{3}{7}\times\dfrac{89}{120}\\ =\dfrac{89}{280}\)
\(\dfrac{3}{7}\times\dfrac{1}{5}+\dfrac{2}{3}\times\dfrac{3}{7}-\dfrac{3}{7}\times\dfrac{1}{8}\)
\(=\dfrac{3}{7}\times\left(\dfrac{1}{5}+\dfrac{3}{7}-\dfrac{1}{8}\right)\)
\(=\dfrac{3}{7}\times\dfrac{56+120-35}{280}\)
\(=\dfrac{3}{7}\times\dfrac{141}{280}\)
\(=\dfrac{423}{1960}\)
Mik có sửa lại đề
C1: \(\dfrac{6}{7}\times\dfrac{1}{2}+\dfrac{6}{7}\times\dfrac{1}{4}=\dfrac{3}{7}+\dfrac{3}{14}=\dfrac{6}{14}+\dfrac{3}{14}=\dfrac{9}{14}\)
C2:\(\dfrac{6}{7}\times\dfrac{1}{2}+\dfrac{6}{7}\times\dfrac{1}{4}=\dfrac{6}{7}\times\left(\dfrac{1}{2}+\dfrac{1}{4}\right)=\dfrac{6}{7}\times\left(\dfrac{2}{4}+\dfrac{1}{4}\right)=\dfrac{6}{7}\times\dfrac{3}{4}=\dfrac{9}{14}\)
5/6 x 1/7 - 1/7 x 1/6
= 1/7 x (5/6 - 1/6)
= 1/7 x 2/3
= 2/21
8/15 : 4/5 x 3/2
= 2/3 x 3/2
= 1
\(\dfrac{1}{5}\times\dfrac{4}{7}+\dfrac{3}{7}\times\dfrac{1}{5}-\dfrac{1}{5}\)
\(=\dfrac{4}{35}+\dfrac{3}{35}-\dfrac{1}{5}\)
\(=\dfrac{7}{35}-\dfrac{1}{5}\)
\(=\dfrac{1}{5}-\dfrac{1}{5}\)
\(=0\)
1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7+1/7x1/8+1/8x1/9
=7/18
\(\frac{4}{7}+x=\frac{5}{7}\cdot\frac{1}{2}\)
\(\frac{4}{7}+x=\frac{5}{14}\)
\(x=\frac{5}{14}-\frac{4}{7}\)
\(x=\frac{5}{14}-\frac{8}{14}\)
\(x=-\frac{3}{14}\)
4/7+x=5/7.1/2
4/7+x=5/14
x=5/14-4/7
x=-3/14