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\(a,x=\dfrac{13}{2}-2\\ x=\dfrac{9}{2}\\ b,x=\dfrac{4}{5}\times\dfrac{3}{4}\\ x=\dfrac{12}{20}=\dfrac{3}{5}\)
\(1\)\(\frac{1}{3}x1\)\(\frac{1}{4}x1\)\(\frac{1}{5}x...x1\)\(\frac{1}{8}\)
\(=\frac{4}{3}x\)\(\frac{5}{4}x\)\(\frac{6}{5}\)\(x...x\)\(\frac{9}{8}\)
Tự tính nốt
\(1\frac{1}{3}\times1\frac{1}{4}\times1\frac{1}{5}\times1\frac{1}{6}\times1\frac{1}{7}\times1\frac{1}{8}.\)
= \(\frac{4}{3}\times\frac{5}{4}\times\frac{6}{5}\times\frac{7}{6}\times\frac{8}{7}\times\frac{9}{8}\times\frac{10}{9}\)
= \(\frac{4\times5\times6\times7\times8\times9\times10}{3\times4\times5\times6\times7\times8\times9}\)
= \(\frac{10}{3}\)
a: \(=167\cdot\dfrac{67}{1000}+167\cdot\dfrac{33}{1000}=167\cdot\dfrac{1}{10}=\dfrac{167}{10}\)
\(\left(x+\dfrac{1}{3}\right)\times\dfrac{9}{14}\times\dfrac{7}{3}-\dfrac{1}{3}=1:\dfrac{9}{5}\\ \Rightarrow\left(x+\dfrac{1}{3}\right)\times\dfrac{3}{2}-\dfrac{1}{3}=\dfrac{5}{9}\\ \Rightarrow\left(x+\dfrac{1}{3}\right)\times\dfrac{3}{2}=\dfrac{5}{9}+\dfrac{1}{3}\\ \Rightarrow\left(x+\dfrac{1}{3}\right)\times\dfrac{3}{2}=\dfrac{8}{9}\\ \Rightarrow x+\dfrac{1}{3}=\dfrac{8}{9}:\dfrac{3}{2}\\ \Rightarrow x+\dfrac{1}{3}=\dfrac{16}{27}\\ \Rightarrow x=\dfrac{16}{27}-\dfrac{1}{3}\\ \Rightarrow x=\dfrac{7}{27}\)
A = 1 x 2 + 2 x 3 + 3 x 4 + 4 x 5 + ... + 99 x 100
A = 2 + 6 + 12 + 20 + ... 9900
A = [2+9900] rồi bn nhân tổng số từ số 2 - 9900
\(3A=1.2.3+2.3.\left(4-1\right)+...+99.100.\left(101-98\right)\)
\(3A=1.2.3+2.3.4-1.2.3+...+99.100.101-98.99.100\)
\(3A=99.100.101\)
\(\Rightarrow A=\frac{99.100.101}{3}\)