\(\left(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+\frac{2}{17x19}+\frac{2}{19x21}\right)\)) x 462 - y = 19

\(=\left(\frac{13-11}{11x13}+\frac{15-13}{13x15}+\frac{17-15}{15x17}+\frac{19-17}{17x19}+\frac{21-19}{19x21}\right)\)x 462 - y = 19

\(=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{21}\)) x 462 - y = 19

\(=\left(\frac{1}{11}-\frac{1}{21}\right)\)x 462 - y = 19

\(=\left(\frac{21}{231}-\frac{11}{231}\right)\)x 462 - y = 19

\(=\frac{10}{231}\)x 462 - y = 19

\(=20\)- y = 19

                y = 20 - 19

                y = 1

Mình làm bài này rồi

Đúng đó

Bài này có trong violympic

thanks pro

Nhưng bn ơiX là x^2 hay tách biệt nếu tách biệt thì là 9/49 còn nếu là x^2 thì là 3/7 nhé

\(=\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{19}-\frac{1}{21}\right)xX=\frac{9}{7} \)\(=\left(\frac{1}{3}-\frac{1}{21}\right)xX=\frac{9}{7}\)\(=\frac{2}{7}xX=\frac{9}{7}\)

\(X=\frac{9}{7}:\frac{2}{7}\)

\(X=\frac{9}{2}\)

bạn @nguyentrinhnganthanh cố giúp mik nha

đáp án là 1

k cho mk nha

là 1

khỏi cần ai giúp nữa nhưng k cho mình nhé

k cho mình

2/(11x13) = 1/11 - 1/13 ; 2/(13x15) = 1/13 - 1/15 ; 2/(15x17) = 1/15 - 1/17 ; 2/(17x19) = 1/17 - 1/19 ; 2/(19x21) = 1/19 - 1/21

2/(11x13) + 2/(13x15) + 2/(15x17) + 2/(17x19) 2/(19x21) =

1/11 - 1/13 + 1/13 - 1/15 + 1/15 - 1/17 + 1/17 - 1/19 + 1/19 - 1/21 = 1/11 - 1/21 = 101231

Hay:   10/231 x 462 - X = 19

20 - X = 19

X = 20 - 19

X = 1

KHÔNG PHẢI = 19 NHA BẠN

(11×132​+13×152​+15×172​+17×192​+19×212​)×462−y=19

⇒(111−113+113−115+115−117+117−119+119−121)×462−�=19⇒(111​−131​+131​−151​+151​−171​+171​−191​+191​−211​)×462−y=19

⇒(111−121)×462−�=19⇒10231×462−�=19⇒(111​−211​)×462−y=19⇒23110​×462−y=19

$\Rightarrow 20-y=19\Rightarrow y=20-19=1$

Tìm \(x\) biết: 

(\(\dfrac{2}{11\times13}\) + \(\dfrac{2}{13\times15}\)+...+ \(\dfrac{2}{19\times21}\)) x 462 - (204: (\(x-105\)):12) =19

(\(\dfrac{1}{11}-\dfrac{1}{13}\)+ \(\dfrac{1}{13}\) - \(\dfrac{1}{15}\)+...+ \(\dfrac{1}{19}\) - \(\dfrac{1}{21}\)) x 462 - (204 : (\(x\) -105):12) =19

(\(\dfrac{1}{11}\) - \(\dfrac{1}{21}\)) x 462 -  \(\dfrac{204:(x-105)}{12}\) = 19

\(\dfrac{10}{213}\) x 462 - \(\dfrac{204:\left(x-105\right)}{12}\) = 19

20 - \(\dfrac{204:\left(x-105\right)}{12}\) = 19

204:(\(x\) - 105):12 = 20 - 19

204:(\(x-105\)):12 = 1

204: (\(x\) - 105) = 12

          \(x-105\) = 204: 12

           \(x\) - 105 = 17

           \(x\)          = 17 + 105

           \(x\)         = 122

\(\left(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+\frac{2}{17.19}+\frac{2}{19.21}\right)\cdot462-x=19\)

\(\Rightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right)\cdot462-x=19\)

\(\Rightarrow\left(\frac{1}{11}-\frac{1}{21}\right)\cdot462-x=19\)

\(\Rightarrow\frac{10}{231}\cdot462-x=19\)

\(\Rightarrow20-x=19\Rightarrow x=1\)

Ta có:

\(\left(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+\frac{2}{17.19}+\frac{2}{19.21}\right).462-x=19\)

\(\Rightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{21}\right).462-x=19\)

\(\Rightarrow\left(\frac{1}{11}-\frac{1}{21}\right).462-x=19\)

\(\Rightarrow\frac{10}{231}.462-x=19\Leftrightarrow20-x=19\)

\(\Rightarrow x=20-19=1\)