已知实数x,y,z满足x-y=5,z^2=-xy-y-9,求x-2y+3z的值
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已知实数x,y,z满足x-y=5,z^2=-xy-y-9,求x-2y+3z的值
已知实数x,y,z满足x-y=5,z^2=-xy-y-9,求x-2y+3z的值
已知实数x,y,z满足x-y=5,z^2=-xy-y-9,求x-2y+3z的值
x-y=5
x=5+y
z^2=-xy-y-9=-(5+y)y-y-9=-y^2-6y-9=-(y+3)^2
所以,z=0,y+3=0
z=0,y=-3
x=5+y=5-3=2
x-2y+3z=2-2*(-3)+0=8
答案=8 把X=5+Y代入Z(平方)=-XY-Y-9会得到Z(的平方)=-(Y+3)的平方
所以两边只能都等0得Z=0 Y=-3 X=2能看懂么
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