Question

TINH GIA TRI BIEU THUC :A=1/30+1/42+1/56+1/72+1/90+1/110+1/132

Answer 1

A=1/30+1/42+1/56+1/72+1/90+1/110+1/132 =1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/11.12 =1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11 =1/5-1/11 =11/55-5/55 =6/55

Answer 2

\(A=\frac{1}{5.6}+\frac{1}{6.7}+\frac{7}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}\)

\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}\)

\(A=\frac{1}{5}-\frac{1}{12}\)

\(A=\frac{7}{60}\)

Answer 3

\(\Rightarrow A=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}\)

\(\Rightarrow A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+......+\frac{1}{11}-\frac{1}{12}\)

\(\Rightarrow A=\frac{1}{5}-\frac{1}{12}=\frac{12}{60}-\frac{5}{60}\)

 \(A=\frac{7}{60}\)