已知1/2x-y=-3,求代数式[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]除以4x的值
问题描述：
已知1/2x-y=-3,求代数式[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]除以4x的值
答
依题意，得
[(9x^2-4y^2)-(5x^2+8xy-4y^2)]/4x＝(4x^2-8xy)/4x＝(x^2-2xy)/x (x≠0)＝x-2y＝2[(x/2)
-y]＝-6
注：仅供参考！
答
[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]÷4x
=(9x²-4y²-5x²-8xy+4y²)/4x
=(4x²-8xy)/4x
=x-2y
=2(1/2x-y)
=2×(-3)
=-6