數學難題13條

１.(-3-x)(-1+x)
=3-3x+x-x2次方
=x2次方-2x+3

２.(2x+1)(3x+1)
=6x2次方+2x+3x+1
= 6x2次方+5x+1

３.(5x-4)(x+2)
=5x2次方+5x-4x-8
=5x2次方+x-8

４.(3x+4)(4x-3)
=12x2次方-9x+8x-12
=12x2次方-x-12

５.(7x-2)(-x+3)
=7x2次方+21x+2x-6
=7x2次方+23x-6

６.(5-3x)(3+2x)
=15+10x-9x-6x2次方
=-6x2次方+x+15

７.(5-2x)(-5-x)
=-25-5x+10x+2x2次方
=2x2次方+5x-25

８.(2x+3y)(x+y)
=2x2次方+2xy+3xy+3y2次方
=2x2次方+5xy+3y2次方

９.(3x-y)(x+2y)
=3x2次方+6xy-xy-2y2次方
=3x2次方+5xy-2y2次方

１０.(x+2y)(2x-y)
=2x2次方-xy+4xy-2y2次方
=2x2次方+3xy-2y2次方

１１.(x-4y)(2y-3x)
=2xy-3x2次方-8y2次方+12xy
=-3x2次方+14xy-8y2次方

１２. -(3y-5x)(y-6x)
=-(3y2次方-18xy-5xy+30x2次方)
=-(30x2次方-23xy+3y2次方)
=-30x2次方+23xy-3y2次方

１３. (-x-y)(-y-x)
=xy+x2次方+y2次方+xy
=x2次方+2xy+y2次方

第一條就做錯，唉～

１.(-3-x)(-1+x)=-(x+3)(x-1)=-(x^2-x+3x-3)=-x^2-2x+3//
２.(2x+1)(3x+1)=6x^2+3x+2x+1=6x^2+5x+1//
３.(5x-4)(x+2)=5x^2-4x+10x-8=5x^2+6x-8//
４.(3x+4)(4x-3)=12x^2-9x+16x-12=12x^2+7-12//
５.(7x-2)(-x+3)=-(7x-2)(x-3)=-(7x^2-21x-2x+6)=-7x^2+23x-6//
６.(5-3x)(3+2x)=15+10x-9x-6x^2=-6x^2+x+15//
７.(5-2x)(-5-x)=(2x-5)(x+5)=2x^2-5x+10x-25=2x^2+5x-25//
８.(2x+3y)(x+y)=2x^2+2xy+3xy+3y^2=2x^2+5xy+3y^2//
９.(3x-y)(x+2y)=3x^2+6xy-xy-2y^2=3x^2+5xy-2y^2//
１０.(x+2y)(2x-y)=2x^2-xy+4xy-2y^2=2x^2+3xy-2y^2//
１１.(x-4y)(2y-3x)=2xy-3x^2-8y^2-12xy=3x^2-10xy-8y^2//
１２. -(3y-5x)(y-6x)=-(3y^2-18xy-5xy+30x^2)=-30x^2+23xy-3y^2//
１３. (-x-y)(-y-x) =(x+y)(x+y)=(x+y)^2=x^2+2xy+y^//