Question

A=5^2/1.6+5^2/6.11+.....+5^2/26.31

Answer 1

\(A=\dfrac{5^2}{1\cdot6}+\dfrac{5^2}{6\cdot11}+...+\dfrac{5^2}{26\cdot31}\)

\(=5\left(\dfrac{5}{1\cdot6}+\dfrac{5}{6\cdot11}+...+\dfrac{5}{26\cdot31}\right)\)

\(=5\left(1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+...+\dfrac{1}{26}-\dfrac{1}{31}\right)\)

\(=5\left(1-\dfrac{1}{31}\right)=5\cdot\dfrac{30}{31}=\dfrac{150}{31}\)

Answer 2

bằng \(\dfrac{5}{3}\)

Answer 3

A=5{5/1.6+5/6.11+.....+5/26.31}

A=5{1-1/6+1/6-1/11+.....+1/26-1/31}

A=5{1-1/31}

A=5.30/31

A=150/31