1.y/{[(x+2y)(x-2y)-(x+2y)^2]/2}
=2y/[(x+2y)(x-2y)-(x+2y)^2]
=2y/[x^2-4y^2-(x^2+4xy+4y^2)]
=2y/[x^2-4y^2-x^2-4xy-4y^2]
=2y/[-4xy-8y^2]
=2y/-4y[x+2y]
=-1/2[x+2y]
将x＝1,y＝1/4代入,得
-1/2[x+2y]
=-1/2[1+2x1/4]
=-1/2[3/2]
=-1/3
2.(2a+b)^2-(2a-b)(a+b)-2(a-2b)(a+2b)
=4a^2+4ab+b^2-(2a^2+2ab-ab-b^2)-2(a^2-4b^2)
=4a^2+4ab+b^2-2a^2-2ab+ab+b^2-2a^2+8b^2
=3ab+10b^2
将a＝2分之1,b＝－2代入,得
3ab+10b^2
=3x1/2x(-2)+10x(-2)^2
=-3+40
=37