若x+y=4,xy=3求x分之y+y分之x

问题描述:

若x+y=4,xy=3求x分之y+y分之x

x分之y+y分之x
=y/x+x/y
=y^2/xy+x^2/xy
=(x^2+y^2)/xy
=[(x+y)^2-2xy]/xy
=(4^2-6)/3
=10/3