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![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\right).462-\left[2,04:\left(x+1,05\right):0,12\right]=19\)
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right):0,12\right]=19\)
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right):0,12\right]=19\)
\(\Leftrightarrow\frac{10}{231}.462-\left[2,04:\left(x+1,05\right):0,12\right]=19\)
\(\Leftrightarrow20-\left[2,04:\left(x+1,05\right):0,12\right]=19\)
\(\Leftrightarrow2,04:\left(x+1,05\right):0,12=1\)
\(\Leftrightarrow2,05:\left(x+1,05\right)=0,12\)
\(\Leftrightarrow x+1,05=\frac{205}{12}\)
\(\Leftrightarrow x=\frac{205}{12}-1,05\)
\(\Leftrightarrow x=\frac{481}{30}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Sao mk câu hỏi của bạn dùng mà tốn giấy vậy, tiết kiệm chút đi
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-...+\frac{1}{19}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\left(\frac{1}{11}-\frac{1}{21}\right).462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\frac{10}{231}.462-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(20-\left[2,04:\left(x+1,05\right)\right]:0,12=19\)
\(\left[2,04:\left(x+1,05\right)\right]:0,12=20-19=1\)
\(2,04:\left(x+1,05\right)=0,12\)
\(x+1,05=2,04:0,12\)
x+1,05=17
x=17-1,05=15,95
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
mk chỉ làm được câu a thôi :
a) gọi A= \(\frac{2}{11.13}+\frac{2}{13.15}+......+\frac{2}{19.21}\)
A= \(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+......+\frac{1}{19}-\frac{1}{21}\)
\(\frac{1}{11}-\frac{1}{21}\)
\(\frac{21}{231}-\frac{11}{231}\)= \(\frac{10}{231}\)
\(\Rightarrow\frac{10}{231}.462-[2,04:\left(x+1,05\right)]:0,12=19\)
20,08 - \([2,04:\left(x+1,05\right)]:0,12=19\)
\(.........\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\right).462-\left[2.04:\left(x+1,5\right)\right]:0,12=19\)
=> \(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right).462-\left[2,04:\left(x+15\right)\right]\) \(:0,12=19\)
=> \(\left(\frac{1}{11}-\frac{1}{21}\right).462-\left[2,04:\left(x+15\right)\right]:0,12=19\)
=> \(\frac{10}{231}.462-\left[2,04:\left(x+15\right)\right]:0,12=19\)
=>\(20-\left[2,04:\left(x+15\right)\right]:0,12=19\)
=>\(\left[2,04:\left(x+15\right)\right]:0,12=20-19=1\)
=> \(2,04:\left(x+15\right)=1.0,12=0,12\)
=> \(x+15=2,04:0,12=17\)
=> \(x=17-15=2\)
Vậy x=2
**** đi @nguyentuantai
Cho góc tù xOy bên trong góc xOy Vẽ tia Om và On. Sao cho goc xOm=90 Độ góc yOn bằng 90 đo
a, Chứng minh rằng góc xOn = góc yom
b, Gọi Ot là tia nằm trong góc xOy sao cho góc xOt = góc tOy
Dài lắm!!!!
oh troi!