\(=\frac{1}{3}.\left(1-\frac{1}{4}\right)+\frac{1}{3}.\left(\frac{1}{4}-\frac{1}{7}\right)+\frac{1}{3}.\left(\frac{1}{7}-\frac{1}{9}\right)+...+\frac{1}{3}.\left(\frac{1}{97}-\frac{1}{100}\right)=\frac{x}{2}\)
\(=\frac{1}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{100}\right)=\frac{x}{2}\)
\(=\frac{1}{3}.\left(1-\frac{1}{100}\right)=\frac{x}{2}\)
\(\frac{1}{3}.\frac{99}{100}=\frac{x}{2}\)
\(\frac{99}{300}=\frac{x}{2}\)
\(x\)ko thỏa mãn
\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.9}+......+\frac{1}{97.100}=\frac{x}{2}\)
\(\Rightarrow\frac{1}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+.....+\frac{1}{97}-\frac{1}{100}\right)=\frac{x}{2}\)
\(\Rightarrow\frac{1}{3}.\left(1-\frac{1}{100}\right)=\frac{x}{2}\Rightarrow\frac{1}{3}.\frac{99}{100}=\frac{x}{2}\Rightarrow\frac{33}{100}=\frac{x}{2}\Rightarrow\frac{33}{100}=\frac{50x}{100}\Rightarrow33=50x\Rightarrow x=\frac{33}{50}\)
\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.9}+...+\frac{1}{97.100}=\frac{x}{2}\)
\(\Leftrightarrow\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.9}+...+\frac{3}{97.100}=\frac{3x}{2}\)
\(\Leftrightarrow1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{100}=\frac{3x}{2}\)
\(\Leftrightarrow1-\frac{1}{100}=\frac{3x}{2}\)
\(\Rightarrow\frac{3x}{2}=\frac{99}{100}\)
\(\Rightarrow3x.100=2.99\)
\(\Rightarrow300x=198\)
\(\Rightarrow x=\frac{198}{300}\)
\(\Rightarrow x=0,66\)
Chúc bạn học giỏi nha!!!
cảm ơn nha nhưng mình ko bít chọn câu nào đây ?
