1.已知X,Y,Z为实数,且X+Y+Z=5,XY+YZ+ZX=3,则Z得取值范围为?

题目

1.已知X,Y,Z为实数,且X+Y+Z=5,XY+YZ+ZX=3,则Z得取值范围为?
2.已知点A（1,3）,B（5,-2）在X轴上找点P,使|AP-BP|最大,则满足条件的点P的坐标是?
3.设X1,X2,X3...X2007为实数,且满足X1X2X3...X2007=X1-X2X3...X2007=X1X2-X3...X2007=X1X2X3...X2006-X2007=1,则X2000的值是

答案

1,x=5-y-z,xy=5y-y^2-yzxy+yz+zx=xy+z(x+y)=5y-y^2-yz +z(5-z)=-y^2+(5-z)y+z(5-z)=3y^2-(5-z)y+3+z^2-5z=0y是实数,所以:判别式:(5-z)^2-4(3+z^2-5z)=-3z^2+10z+13≥0,3z^2-10z-13=(3z-13)(z+1)≤0,-1≤z≤13/32,作B...