59. =(a(a+b) -(a-b)(a-b)) /(a+b)(a-b) =(a²+ab-a²+2ab-b²) /(a+b)(a-b) =(3ab -b²)/(a²-b²)60. =((x-y)(x-y) -y(x+y)) /(x+y)(x-y) =(x²-2xy+y²-xy-y²) /(x² -y²) =(x² -3xy) /(x² -y²)67. y² -x² =(y -x)(y+x)(4y -2(y+x)) /(y-x)(y+x) =(4y -2y -2x) /(y -x)(y+x) =(2y -2x) /(y-x)(y+x) =2(y-x) /(y-x)(y+x) =2/(y+x)73. ((a-c)(a+c) -c(a-c)) /c(a+c) =(a² -c² -ac +c²) /c(a+c) =(a² -ac) /c(a+c)