Chứng ming rằng : f(x ; y) =$x^{2}+5y^{2}-4xy+2x-6y+3>0$
CMR : f(x ; y) =$x^{2}+5y^{2}-4xy+2x-6y+3>0$
Started By cold_noodles97, 30-03-2012 - 19:16
#2
Posted 30-03-2012 - 19:39
WhjteShadow
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Thượng úy
Ta có $x^2+5y^2-4xy+2x-6y+3= (x-2y+1)^2+(y-1)^2+1> 0$ Đúng với mọi x,y 
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