a. xxy+y2−yx2+xy
= xy(x+y)−yx(x+y)
= x.xy(x+y).x−y.yx(x+y).y
= x2−y2xy(x+y)
= (x−y)(x+y)xy(x+y)
= x−yxy
b. x2+4x2−4−xx+2−x2−x
= x2+4(x−2)(x+2)−x(x−2)(x+2)(x−2)−x(x+2)(x−2)(x+2)
= x2+4−x2+2x−x2−2x(x−2)(x+2)
= 4−x2(x−2)(x+2)
= −(x−2)(x+2)(x−2)(x+2)=−1
c. a2+abb−a:a+b2a2−2b2
= a(a+b)b−a.2(a−b)(a+b)a+b
= a(a+b).2(a−b)b−a
= a(a+b).(−2)(b−a)b−a
= −2a2−2ab
d. (2x+12x−1−2x−12x+1):4x10x−5
= ((2x+1)(2x+1)(2x−1)(2x+1)−(2x−1)(2x−1)(2x+1)(2x−1)):4x10x−5
= (2x+1)2−(2x−1)2(2x+1)(2x−1):4x10x−5
= ((2x)2+2.2x+12)−((2x)2−2.2x+12)(2x+1)(2x−1):4x10x−5
= 4x2+4x+1−4x2+4x−1(2x+1)(2x−1):4x10x−5
= 8x(2x+1)(2x−1).5(2x−1)4x
= 102x+1