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=?

x=5-y z2=-y2+6y-9=-(y-3)2 z=0 y=3 x=2 x+2y+3z=8