Question

求值（x^2+xy)/(x^2-2xy-3y^2)*(3y-x)/(x-y)+(x^-1+y^-1)÷(x^-1-y^-1),其中x=2，y=-1

Answer 1

原式=[x(x+y)/(x-3y)(x+y)][-(x-3y)/(x-y)]+(1/岩猛x+1/y)/改枣磨(1/x-1/y)
=-x/(x-y)+(y+x)/核斗(y-x)
=(2x+y)/(y-x)
=3/(-3)
=-1

Answer 2

原式缺哗=xy(y^4-1)
=xy(x²+1)(x²伏槐行-1)
=xy(x²+1)(x+1)(x-1)
原式=[4(a-b)]²明枯-[5(a+b)]²
=(4a-4b)²-(5a+5b)
=(4a-4b+5a+5b)(4a-4b-5a-5b)
=-(9a+b)(a+9b)