2 replies to this topic

[dungCT]

Cho x,y,z dương thõa mãn :xy+yz+xz=1.Chứng minh rằng:
x(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?y^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?z^2)+y(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?x^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?z^2)+z(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?x^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?y^2) http://dientuvietnam.net/cgi-bin/mimetex.cgi?\dfrac{4\sqrt{3}}{9}

[chuyentoan]

Bài này dùng lượng giác là được. Hình như là một bài thi của TQ thì phải

[beati-car]

Cho x,y,z dương thõa mãn :xy+yz+xz=1.Chứng minh rằng:
x(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?y^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?z^2)+y(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?x^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?z^2)+z(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?x^2)(1-http://dientuvietnam.net/cgi-bin/mimetex.cgi?y^2) http://dientuvietnam.net/cgi-bin/mimetex.cgi?\dfrac{4\sqrt{3}}{9}

mot bai don gian nhin dieu kien la biet dung l­uong giac roi