\(E=\dfrac{1}{1\times2}+\dfrac{2}{2\times4}+\dfrac{3}{4\times7}+\dfrac{4}{7\times11}+\dfrac{5}{11\times16}\)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}\)
\(=1-\dfrac{1}{16}=\dfrac{15}{16}\)
#kễnh

\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+...+\dfrac{1}{56}-\dfrac{1}{67}\)

\(=1-\dfrac{1}{67}=\dfrac{66}{67}\)

Từng câu hay toán bình dương zậy

\(\dfrac{1}{1\times2}+\dfrac{2}{2\times4}+\dfrac{3}{4\times7}+\dfrac{4}{7\times11}+....+\dfrac{11}{56\times67}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+....+\dfrac{1}{56}-\dfrac{1}{67}\)

\(=1-\dfrac{1}{67}\)

\(=\dfrac{1}{66}\)

biể thức trên = 1/1 - 1/2 + 1/2 - 1/4 + 1/7 +.....+ 1/11 - 1/67

= 1/1 - 1/67 = 66/67

A=1/1-1/2+1/2-1/4+1/4-1/7+1/7-1/11+1/11-1/16+1/16-1/22+1/22-1/29

A=1/1-1/29

A=28/29

55/56

mình cần kết quả

nhầm nhầm mình cần bài giải

a=4099/308

b=2/5/186

Gọi biểu thức trên là A, ta có:

A = 1/1x2 + 2/2x4 + 3/4x7 + 4/7x11 + 5/11x16

A = 1 - 1/2 + 1/2 - 1/4 + 1/4 - 1/7 + 1/7 - 1/11 + 1/11 - 1/16

A = 1 - 1/16 = 15/16

Đặt \(A=\frac{1}{2}+\frac{2}{2\cdot4}+\frac{3}{4\cdot7}+\frac{4}{7\cdot11}+\frac{5}{11\cdot16}\)

\(\Rightarrow A=\frac{1}{1.2}+\frac{2}{2.4}+\frac{3}{4.7}+\frac{4}{7.11}+\frac{5}{11.16}\)

\(\Rightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}\)

\(\Rightarrow A=1-\frac{1}{16}\)

\(\Rightarrow A=\frac{15}{16}\)

k đúng cho mình nhé bạn nhé

hay quá ^_^

ở đâu vậy bạn

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