[(x+2y)^2-(x-y)(x+2y)-5y^2]÷(2y)
=[(x²+4xy+4y²)-(x²+2xy-xy-2y²)-5y²]÷(2y)
=(x²+4xy+4y²-x²-2xy+xy+2y²-5y²)÷(2y)
=(3xy+y²)÷(2y)
=(3x+y)/2