x + y = 2
=>(x - 1) + (y - 1) = 0
=> x - 1 đối y - 1
=> (x - 1)(y - 1)
=> (x - 1)(y - 1) ≤ 0
=> xy - x - y + 1 ≤ 0
=> xy - (x + y) + 1 ≤ 0
=> xy - 2 + 1 ≤ 0
=> xy - 1 ≤ 0
=> xy < 1 (đpcm)
cho x+y=2 chung minh rang xy<1
cho a=x 3y, b=x 2y 2, c=xy 3 .Chung minh rang voi moi so huu ti x va y ta luon duoc ax+b 2-2x 4y 4=0
Cho x + y = 2.Chứng minh\(xy\le1\)
Cho: x+y=2. Chứng minh rằng xy\(\le1\)
Bai1:
1) Tìm x;y;z biết; (xy+1)/9=(xz+2)/15=(yz+3)/27 và xy+xz+yz=11
2) Biết (bz-cy)/a= (cx-az)/b=(ay-bx)/c (a,b,c khong bang 0). Chung minh rang x/a=y/b=z/c
cho x2 + xy + \(\frac{y^2}{3}\)=25 ; z2+ \(\frac{y^2}{3}=9,x^2+xz+z^2=16\)
chung minh rang \(\frac{2z}{x}=\frac{y+z}{x+z}\)
chung minh rang khong ton tai 3 so huu ti :x,y,z
xy=13/15
yz=1/3
zx=3/13
chung minh rang :B=x.y(x^2-y^2).(x^2+y^2)chia het cho 30 (x;y la so nguyen)
cho cac so x,y,z thoa man x/2013=y/2014=z/2015 chung minh rang 4(x-y)(y-z)=(z-x)^2
