已知实数x、y、z满足x+y=5及z=xy+y-9 则x+2y+3z=?
问题描述:
已知实数x、y、z满足x+y=5及z=xy+y-9 则x+2y+3z=?
答
x=5-y z2=-y2+6y-9=-(y-3)2 z=0 y=3 x=2 x+2y+3z=8
已知实数x、y、z满足x+y=5及z=xy+y-9 则x+2y+3z=?
x=5-y z2=-y2+6y-9=-(y-3)2 z=0 y=3 x=2 x+2y+3z=8