Question

[☆MĭηɦღAηɦ❄]

Cau 1 .Cho A = 3/4 + 8/9 + 15/16 +…+ 9999/10000

Chung to a lon hon 4/3

CAU 2 . A = x/x+y + y/y+z +x/x+z

Cho z , y z thuoc N* chung to A k thuoc N

Answer 1

[☆MĭηɦღAηɦ❄]

Cau 2.la z/ x +z chu k phai x / x+z nha mk nham

Answer 2

[『 Trần Diệu Linh 』]

Xin lỗi biết làm câu 1 thôi,thông cảm

Ta có A=:

\(=\frac{2^2-1}{2^2}+\frac{3^2-1}{3^2}+\frac{4^2-1}{4^2}+...+\frac{100^2-1}{100^2}\)

\(=\frac{2^2}{2^2}+\frac{3^2}{3^2}+...+\frac{100^2}{100^2}-\left(\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{100^2}\right)\)

\(=99-\left(\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{100^2}\right)\)

Mà \(\left(\frac{1}{2^2}+\frac{1}{3^2}+....+\frac{1}{100^2}\right)< |\frac{100}{101}\)(tự tính)

\(\Rightarrow C>98\left(đpcm\right)\)