Question

cho số hữu tỉ x thỏa mãn : 6/7-(x-1/2)=5/6.khi đó 21x=?các bạn giúp mình với nha..

Answer 1

\(\frac{6}{7}-\left(x-\frac{1}{2}\right)=\frac{5}{6}\)

\(\frac{6}{7}-x+\frac{1}{2}=\frac{5}{6}\)

\(-x=\frac{5}{6}-\frac{6}{7}-\frac{1}{2}\)

\(-x=\frac{35}{42}-\frac{36}{42}-\frac{21}{42}\)

\(-x=-\frac{22}{42}\)

\(x=\frac{11}{21}\)

\(\Rightarrow21\times x=21\times\frac{11}{21}=11\)

Answer 2

\(\frac{6}{7}-\left(x-\frac{1}{2}\right)=\frac{5}{6}\)

\(x-\frac{1}{2}=\frac{6}{7}-\frac{5}{6}\)

\(x-\frac{1}{2}=\frac{1}{42}\)

\(x=\frac{1}{42}+\frac{1}{2}=\frac{11}{21}\)

Vậy \(21x=21\times\frac{11}{21}=11\)