若x+2y+z=0,5x+4y-4z=0,求(x^2+ 6y^(2 )-10z^2)/(3x^2 -4y^2+5z^2 )的值
问题描述:
若x+2y+z=0,5x+4y-4z=0,求(x^2+ 6y^(2 )-10z^2)/(3x^2 -4y^2+5z^2 )的值
若x+2y+z=0,5x+4y-4z=0,求(x^2+ 6y^(2)-10z^2)/(3x^2-4y^2+5z^2 )的值,
答
2x+4y+2z=05x+4y-4z=03x=6zx=2zy=-(3/2)z代入(x^2+ 6y^2-10z^2)/(3x^2-4y^2+5z^2)=(4zz+6(-3/2z)^2-10zz)/(3(2z)^2-4(-3/2z)^2+5zz)=(4-13.5-10)/(12-9+5)=(-19.5)/(8)=-39/16