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\(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-...+\frac{1}{19}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\left(\frac{1}{11}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\frac{10}{231}.462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(20-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\left[2,04:\left(x+1,05\right)\right]:0,12=20-19=1\)
\(2,04:\left(x+1,05\right)=0,12\)
\(x+1,05=2,04:0,12\)
x+1,05=17
x=17-1,05=15,95
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right).462-\frac{17}{x+1,05}=19.\)
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{21}\right)462-\frac{17}{x+1,05}=19\)
\(\Leftrightarrow20-\frac{17}{x+1,05}=19\)
\(\Leftrightarrow1-\frac{17}{x+1,05}=0\)
\(\Leftrightarrow x+1,05=17\)
\(\Leftrightarrow x=15,95\)
\(\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.20}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(=\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{20}\right)-x=\frac{4}{3}-\frac{221}{231}\)
\(=\left(\frac{1}{11}-\frac{1}{20}\right)-x=\frac{29}{77}\)
\(=\frac{9}{220}-x=\frac{29}{77}\)
\(x=\frac{9}{220}-\frac{29}{77}\)
bạn ơi chỗ \(\frac{2}{19.20}\) có phải là \(\frac{2}{19.21}\) không
\(b.\frac{1}{3}+\frac{3}{35}< \frac{x}{210}< \frac{4}{7}+\frac{3}{5}+\frac{1}{3}\)
\(\Leftrightarrow\frac{35+9}{105}< \frac{x}{210}< \frac{60+63+35}{105}\)
\(\Leftrightarrow\frac{44}{105}< \frac{x}{210}< \frac{158}{105}\)
\(\Leftrightarrow\frac{88}{210}< \frac{x}{210}< \frac{316}{210}\)
Suy ra \(x\in\left\{89;90;100;...;313;314;315\right\}\)
\(c.\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(\Leftrightarrow\frac{1}{11}-\frac{1}{21}-x+\frac{221}{231}=\frac{4}{3}\)
\(\Leftrightarrow\frac{21-11-231x+221}{231}=\frac{308}{231}\)
\(\Leftrightarrow-231x=308-21+11-221\)
\(\Leftrightarrow-231x=77\)
\(\Leftrightarrow x=-\frac{77}{231}=-\frac{1}{3}\)
^^
Ta có:
\(\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\right).231-\left(3^{16}:3^{14}-2^8:2^6\right).x=2013^0\)
\(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right).231-\left(3^2-2^2\right).x=1\)
\(\left(\frac{1}{11}-\frac{1}{21}\right).231-x=1\)
\(\frac{10}{231}.231-x=1\)
\(10-x=1\)
\(x=9\)
Vậy,.............
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