C>D, chắc chắn đó

A = \(\frac{100^{100}+1}{100^{90}+1}\)

\(\frac{1}{100^{10}}A=\frac{100^{100}+1}{100^{100}+100^{10}}\)

\(\frac{1}{100^{10}}A=\frac{100^{100}+100^{10}-100^{10}+1}{100^{100}+100^{10}}\)

\(\frac{1}{100^{10}}A=1+\frac{-100^{10}+1}{100^{100}+100^{10}}\)

B = \(\frac{100^{99}+1}{100^{89}+1}\)

\(\frac{1}{100^{10}}B=\frac{100^{99}+1}{100^{99}+100^{10}}\)

\(\frac{1}{100^{10}}B=\frac{100^{99}+100^{10}-100^{10}+1}{100^{99}+100^{10}}\)

\(\frac{1}{100^{10}}B=1+\frac{-100^{10}+1}{100^{99}+100^{10}}\)

Vì \(\frac{-100^{10}+1}{100^{100}+100^{10}}< \frac{-100^{10}+1}{100^{99}+10^{10}}\)nên A < B

Easy.

Ta có: Nếu \(\frac{a}{b}>1\)thì \(\frac{a}{b}>\frac{a+m}{b+m}\left(m>0\right)\)   (bạn tự c/m)

Mặt khác,ta có: \(C=\frac{2016^{99}+1}{2016^{89}+1}=\frac{2016\left(2016^{99}+1\right)}{2016\left(2016^{89}+1\right)}\)

\(=\frac{2016^{100}+2016}{2016^{90}+2016}=\frac{\left(2016^{100}+1\right)+2015}{\left(2016^{90}+1\right)+2015}\)

Mà \(\frac{\left(2016^{100}+1\right)+2015}{\left(2016^{90}+1\right)+2015}>1\)

Nên \(C=\frac{\left(2016^{100}+1\right)+2015}{\left(2016^{90}+1\right)+2015}< \frac{2016^{100}+1}{2016^{90}+1}=B\)

Vậy \(B>C\)

bằng nhau

bằng nhau

2 vế bằng nhau

100-(1+1/2+1/3+...+1/100) = 1/2+2/3+3/4+...+99/100

100- 1-1/2-1/3-...-1/100 = 1/2+2/3+3/4+...+99/100

100 = 1 + 1/2 + 1/2 + 1/3 + 2/3 + ... + 1/100 + 99/100 (cùng cộng 2 vế với (- 1-1/2-1/3-...-1/100)

100 = 1 + 1 + 1 + ... + 1 (100 số hạng)

100 = 100

Vậy   100-(1+1/2+1/3+...+1/100) = 1/2+2/3+3/4+...+99/100

Cảm ơn bạn!

mk chưa học