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![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2:
a: \(=248+2064-12-236\)
\(=12-12+2064=2064\)
b: \(=-298-302-300=-600-300=-900\)
c: \(=5-7+9-11+13-15=-2-2-2=-6\)
d: \(=456+58-456-38=20\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(=\dfrac{54-34}{189-119}=\dfrac{20}{70}=\dfrac{2}{7}\)
b: \(=\dfrac{6+6\cdot4+6\cdot49}{15+15\cdot4+15\cdot49}=\dfrac{6}{15}=\dfrac{2}{5}\)
c: \(=\dfrac{13\left(3-18\right)}{40\left(15-2\right)}=\dfrac{-15}{40}=-\dfrac{3}{8}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\Leftrightarrow\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+...+\dfrac{1}{19}-\dfrac{1}{21}\right)\cdot462-y=19\)
\(\Leftrightarrow20-y=19\)
hay y=1
![](https://rs.olm.vn/images/avt/0.png?1311)
A = (1- 2) \(\times\) ( 4 - 3) \(\times\) (5 - 6) \(\times\) (8 - 7) \(\times\) (9 - 10) \(\times\) (12 - 11) \(\times\)(13 - 14)
A = (-1) \(\times\) 1 \(\times\) (-1) \(\times\) 1 \(\times\) (-1) \(\times\) 1 \(\times\) (-1)
A = 1
![](https://rs.olm.vn/images/avt/0.png?1311)
\(P=sin^2x+3cos^2x=1-cos^2x+3cos^2x=1+2cos^2x=1+2.\left(\dfrac{1}{4}\right)^2=\dfrac{9}{8}\)
b: \(=\dfrac{-5}{7}\left(\dfrac{2}{11}+\dfrac{9}{11}\right)+\dfrac{13}{4}=\dfrac{-5}{7}+\dfrac{13}{4}=\dfrac{-20+91}{28}=\dfrac{71}{28}\)
c: \(=\dfrac{146}{13}-3-\dfrac{68}{13}=6-3=3\)
d: \(=\dfrac{2}{7}\left(\dfrac{21}{4}-\dfrac{13}{4}\right)=\dfrac{4}{7}\)