3.8^2
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\(\dfrac{3}{4}:\dfrac{2}{3}\times\dfrac{8}{9}\)
\(=\dfrac{3}{4}\times\dfrac{3}{2}\times\dfrac{8}{9}\)
\(=\dfrac{3\times3\times8}{4\times2\times9}\)
\(=\dfrac{9\times8}{9\times8}\)
\(=1\)
\(\dfrac{3}{4}\): \(\dfrac{2}{3}\)x \(\dfrac{8}{9}\)
= \(\dfrac{3}{4}\) x \(\dfrac{3}{2}\) x \(\dfrac{8}{9}\)
= \(\dfrac{9}{8}\) x \(\dfrac{8}{9}\)
= 1
![](https://rs.olm.vn/images/avt/0.png?1311)
Có \(\frac{5^2}{3.8}+\frac{5^2}{8.13}+\frac{5^2}{13.18}+.....+\frac{5^2}{88.93}\)
=\(\frac{5.5}{3.8}+\frac{5.5}{8.13}+\frac{5.5}{13.18}+...+\frac{5.5}{88.93}\)
= \(5\left(\frac{5}{3.8}+\frac{5}{8.13}+\frac{5}{13.18}+...+\frac{5}{88.93}\right)\)
=\(5\left(\frac{1}{3}-\frac{1}{8}+\frac{1}{8}-\frac{1}{13}+\frac{1}{13}-\frac{1}{18}+.....+\frac{1}{88}-\frac{1}{93}\right)\)
=\(5\left(\frac{1}{3}-\frac{1}{93}\right)=\frac{50}{31}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{x}{y}=\frac{2}{5}\)\(\Rightarrow\)\(\frac{x}{2}=\frac{y}{5}\)hay \(\frac{0,2x}{0,4}=\frac{0,3y}{1,5}\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\frac{0,2x}{0,4}=\frac{0,3y}{1,5}=\frac{0,2x+0,3y}{0,4+1,5}=\frac{3,8}{1,9}=2\)
suy ra: \(\frac{0,2x}{0,4}=2\)\(\Rightarrow\)\(x=4\)
\(\frac{0,3y}{1,5}=2\) \(\Rightarrow\)\(y=10\)
![](https://rs.olm.vn/images/avt/0.png?1311)
theo giả thiết
\(\angle\left(A1\right)-2\angle\left(A2\right)=\angle\left(B1\right)-2\angle\left(B2\right)\)
\(< =>180-3\angle\left(A2\right)=180-3\angle\left(B2\right)\)
\(< =>-3\angle\left(A2\right)+3\angle\left(B2\right)=0\)
\(< =>-3\left[\angle\left(A2\right)-\angle\left(B2\right)\right]=0\)
điều này xảy ra\(< =>\angle\left(A2\right)=\angle\left(B2\right)\)
2 góc ở vt so le trong \(=>dpcm\)
3.82 = 3.64 = 192
=192