[(x-2y)平方+(x-2y)(x+2y)-2x(2x-y)]除以(-2x) 其中x=2分之1,y=3 这题怎么算?

[(x-2y)²+(x-2y)(x+2y)-2x(2x-y)]÷(-2x)
=[(x-2y)（x-2y+x+2y)-2x(2x-y)]÷(-2x)
=2x（x-2y-2x+y)÷(-2x)
=-(-x-y)
=x+y
=½+3
=3.5