Question

D= 5phần 1×6 + 5phần 6×11 + 5 phần 11×16 + .....+ 5phần 86×91

Giúp mình nhé!😘😘

Answer 1

Tính

\(D=\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{5}{86.91}\)

\(=1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{86}-\frac{1}{91}\)

\(=1-\frac{1}{91}=\frac{91}{91}-\frac{1}{91}=\frac{90}{91}\)

Vậy \(D=\frac{90}{91}.\)

Answer 2

\(D=\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{5}{86.91}\)

\(=1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+....+\frac{1}{86}-\frac{1}{91}\)

\(=1-\frac{1}{91}\)

\(=\frac{91}{91}-\frac{1}{91}\)

\(=\frac{90}{91}\)

Vậy \(D=\frac{90}{91}\)

Chúc bạn học tốt !