已知xy除以x+y=2,求代数3x-5y+3y除以-x+3xy-y的值?123456

Question

已知xy除以x+y=2,求代数3x-5y+3y除以-x+3xy-y的值?
123456

Answer 1

此题应该抄错了,应该是遗漏了一个x,
∵ xy/(x+y) = 2
∴ 1/x + 1/y = 1/2
(3x - 5xy + 3y)/(-x + 3xy -y)
=(3x - 5xy + 3y)/(-x + 3xy -y) [分子分母同除以xy,得]
=(3/x + 3/y - 5)/(-1/x - 1/y + 3)
=(3/2 -5)/(-1/2 + 3)
=-7/5