Question

A= 1/2+1/6+1/12+1/20+...+1/132+1/156

B= 1/10+1/15+1/21+...+1/66+1/78+1/91+1/105

C= 1/2+5/6+11/12+...+109/110+...+599/600+649/650

cíu mìn zớiiii

Answer 1

\(A=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{11}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{13}=\dfrac{12}{13}\)

\(B=\dfrac{2}{20}+\dfrac{2}{30}+...+\dfrac{2}{210}\)

\(=2\left(\dfrac{1}{20}+\dfrac{1}{30}+...+\dfrac{1}{210}\right)\)

\(=2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-...+\dfrac{1}{14}-\dfrac{1}{15}\right)\)

\(=2\cdot\dfrac{11}{60}=\dfrac{11}{30}\)