已知实数z、y、z满足x+y=5及z2=xy+y-9,则x+2y+3z=_.
已知实数z、y、z满足x+y=5及z2=xy+y-9,则x+2y+3z=______.
数学人气:165 ℃时间:2019-10-18 17:07:20
优质解答
∵x+y=5,z2=xy+y-9,
∴x=5-y,
代入z2=xy+y-9得:z2=(5-y)y+y-9,
z2+(y-3)2=0,
z=0,y-3=0,
∴y=3,x=5-3=2,
x+2y+3z=2+2×3+3×0=8,
故答案为8.
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