B=\(\left(\dfrac{151515}{161616}+\dfrac{17^9}{17^{10}}\right)-\left(\dfrac{1500}{1600}-\dfrac{176}{187}\right)\). tinh nhanh

1 mảnh vườn HCN co CR=70 m . biết\(\dfrac{4}{7}\)CR=\(\dfrac{5}{13}\)CD.tinh dien tich va chu vi

\(\dfrac{3}{4}+\dfrac{8}{9}+\dfrac{15}{16}+...+\dfrac{399}{400}.CM\) ko la so nguyen duong

\(\dfrac{1}{1+2+3}+\dfrac{1}{1+2+3+4}+...+\dfrac{1}{1+2+3+...+99}< \dfrac{2}{3}\)

\(\dfrac{3}{4!}+\dfrac{3}{5!}+...+\dfrac{3}{100!}< \dfrac{1}{3!}\)

tim x

-(4x-1)-(5x+1)-(1-3x)=4.(2x-1)+6

CMR ; B=10ⁿ + 72n - 1 ⋮ 81

19 nha bạn 

chữ cuối là chữ quà mà

\(\dfrac{1}{200}< \dfrac{1}{100^2}+\dfrac{1}{101^2}+...+\dfrac{1}{199^2}< \dfrac{1}{99}\)

\(\dfrac{x}{y}=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{1329}-\dfrac{1}{1330}+\dfrac{1}{1331}\)

CM x⋮ 1997