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Nhân thêm 2
=>(13-11/11x13+...+21-19/19x21)-x+221/231=4/3
=>(13/11x13-11/11x13+...+21/19x21-19/19x21)-x+221/231=4/3
=>(1/11-1/13+...+1/18-1/21)-x+221/231=4/3
=>(1/11-1/21)-x+221/231=4/3
=>10/231-x+221/231=4/3
=>10/231+221/231-x=4/3
=>231/231-x=4/3
=>1-x=4/3
=>x=1-4/3=-1/3
=2/11+2/13-2/13+2/15-2/15+...-2/97+2/98
=2/11+(2/13-2/13+2/15-2/15+...-2/97+2/99)
=2/11+2/99
=20/99
\(\frac{2}{11}\times13+\frac{2}{13}\times15+\frac{2}{15}\times17+........+\frac{2}{97}\times99\)
\(A\times2=\frac{2}{11\times13}+\frac{2}{13\times15}+\frac{2}{15\times17}+........+\frac{2}{97\times99}\)
\(A\times2=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+........+\frac{1}{97}-\frac{1}{99}\)
\(A=\frac{1}{11}-\frac{1}{99}\)
\(A=\frac{8}{99}\)
mik ko bt là có đúng hay ko nhưng đúng thì các bạn cho 1 t i c k nha
2/11x13+2/13x15+2/15x17+...+2/97x99
=1/11-1/13+1/13-1/15+1/15-1/17+...+1/97-1/99
=1/11-1/99
=8/99
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
\(=\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{19}-\frac{1}{21}\right)xX=\frac{9}{7} \)\(=\left(\frac{1}{3}-\frac{1}{21}\right)xX=\frac{9}{7}\)\(=\frac{2}{7}xX=\frac{9}{7}\)
\(X=\frac{9}{7}:\frac{2}{7}\)
\(X=\frac{9}{2}\)
(1/11-1/13+1/13-1/15+.....+1/19-1/21)*462-y=19
(1/11-1/21)*462-y=19
10/231*462-y=19
20-y=19
y=1
\(\left(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+\frac{2}{17x19}+\frac{2}{19x21}\right)\)) 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
\(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+...+\frac{2}{97x99}\)
\(=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{97}-\frac{1}{99}\)
\(=\frac{1}{11}-\frac{1}{99}\)
\(=\frac{8}{99}\)