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![](https://rs.olm.vn/images/avt/0.png?1311)
b: \(=\dfrac{x+5+x+x-5}{x\left(x+5\right)}=\dfrac{3x}{x\left(x+5\right)}=\dfrac{3}{x+5}\)
\(a,=-3x^3+x^2+9x^2-3x-12x+4=-3x^3+10x^2-15x+4\\ b,=\dfrac{x+5+x+x-5}{x\left(x+5\right)}=\dfrac{3x}{x\left(x+5\right)}=\dfrac{3}{x+5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1) \(x-y=3\\ \Rightarrow\left(x-y\right)^2=3^2\\ \Rightarrow x^2-2xy+y^2=9\\ \Rightarrow\left(x^2+y^2\right)-2xy=9\\ \Rightarrow x^2+y^2=9+2xy\)
\(\Rightarrow x^2+y^2=9-4\)(vì xy=-2)
\(\Rightarrow x^2+y^2=5\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x=\frac{1}{2}\frac{\sqrt{\left(\sqrt{2}-1\right)^2}}{\sqrt{\left(\sqrt{2}-1\right)\left(\sqrt{2}+1\right)}}=\frac{1}{2}.\left(\sqrt{2}-1\right)\)
\(\Rightarrow2x=\sqrt{2}-1\Rightarrow2x+1=\sqrt{2}\)
\(\Rightarrow4x^2+4x+1=2\Rightarrow4x^2+4x-1=0\)
\(B=\left[x^3\left(4x^2+4x-1\right)-x\left(4x^2+4x-1\right)+4x^2+4x-1-1\right]^{2018}+2018\)
\(=\left(-1\right)^{2018}+2018=2019\)
![](https://rs.olm.vn/images/avt/0.png?1311)
https://vi.scribd.com/document/323989515/50-%C4%91%E1%BB%81-thi-olympic-toan-2000-pdf
tham khảo ở link này (mình gửi cho)
Học tốt!!!!!!!!!!!!!
a) 79.28.9 + 21.28.9
= 28.9(79 + 21)
= 28.9.100
= 252.100 = 25200
b) 162 + 4.8.34 + 342
= 162 + 2.2.8.34 + 342
= 162 + 2.16.34 + 342
= (16 + 34)2
= 502 = 2500
c) 410.510 - (205 - 2)(205 + 2)
= 410.510 - 2010 + 4
= 410.510 - (4.5)10 + 4
= 410.510 - 410.510 + 4
= 4