\(\frac{3}{1^2.2^2}+\frac{5}{2^2.3^2}+....+\frac{4031}{2015^2.2016^2}=\frac{1}{1^2}-\frac{1}{2^2}+\frac{1}{2^2}-.....-\frac{1}{2016^2}=1-\frac{1}{2016^2}\)

\(\frac{1}{2016^2}>0\Rightarrow A< 1\left(ĐPCM\right)\)

bạn chờ xíu mk lm câu sau nha

Bạn chờ xíu mk lm cho xong nha

\(\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}+\dfrac{7}{3^2.4^2}+...+\dfrac{19}{9^2.10^2}\)

\(=\dfrac{3}{1.4}+\dfrac{5}{4.9}+\dfrac{7}{9.16}+...+\dfrac{19}{81.100}\)

\(=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{16}+...+\dfrac{1}{81}-\dfrac{1}{100}\)

\(=1-\dfrac{1}{100}< 1\left(dpcm\right)\) 

CS AI XEM S** KO

\(\frac{3}{1^2.2^2}+\frac{5}{2^2.3^2}+\frac{7}{3^2.4^2}+...+\frac{19}{9^2.10^2}\)

\(=\left(\frac{1}{1^2}-\frac{1}{2^2}\right)+\left(\frac{1}{2^2}-\frac{1}{3^2}\right)+\left(\frac{1}{3^2}-\frac{1}{4^2}\right)+...+\left(\frac{1}{9^2}-\frac{1}{10^2}\right)\)

\(=\frac{1}{1}-\frac{1}{10^2}\)

\(=1-\frac{1}{100}

=3/1.4+5/4.9+7/9.16+......+19/81.100

=(1/1-1/4)+(1/4-1/9)+........+(1/81-1/100)

=1-1/100

=99/100<1(đpcm)

\(\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}+\dfrac{7}{3^2.4^2}+...+\dfrac{19}{9^2.10^2}\)

\(=\dfrac{3}{1.4}+\dfrac{5}{4.9}+\dfrac{7}{9.16}+...+\dfrac{19}{81.100}\)\(=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{16}+...+\dfrac{1}{81}-\dfrac{1}{100}\)

\(=1-\dfrac{1}{100}< 1\)