【(3x+2y)(3x-2y)-(x+2y)(5x-2y)】÷8x
=【(3x)^2-(2y)^2-(5x^2+8xy-4y^2)】÷8x
=【9x^2-4y^2-5x^2-8xy+4y^2】÷8x
=【4x^2-8xy】÷8x
=【4x-8y】÷8
=x/2-y