— .计算(1)x+2y/x^2-y^2 — x+2y/x^2y^2 — 2x-3y/y^2-x^2还有题在下面

(x+2y)/(x^2 - y^2) - (x+2y)/(x^2 - y^2) - (2x-3y)/(y^2 - x^2)

= (x+2y - x - 2y + 2x - 3y)/(x^2 - y^2)

= (2x - 3y)/[(x-y)(x+y)]

(3m^2 - 5m)/(m^2 - 1) - (2m^2 - 5m + 1)/(m^2 - 1) - (2m^2 - 2)/(1 - m^2)

= (3m^2 - 5m - 2m^2 + 5m - 1 + 2m^2 - 2)/(m^2 - 1)

= (3m^2 - 3)/(m^2 - 1)

= 3

1/(a-2) - 12/(a^2 - 4)

= (a+2 - 12)/(a^2 - 4)

= (a-10)/[(a+2)(a-2)]

3y/(x+y) + y/(y-x) + 2x/(x^2 - y^2)

= [3y(x-y) - y(x+y) + 2x]/(x^2 - y^2)

= [3xy - 3y^2 - xy - y^2 + 2x]/(x^2 - y^2)

= [2xy - 4y^2 + 2x]/(x^2 - y^2)

= 2(xy - 2y^2 + x)/[(x-y)(x+y)]

(a+2)/(a^2 - 4a + 4) - 1/(2a+4) - (a-1)/(2a^2 - 8)

= (a+2)/(a-2)^2 - 1/[2(a+2)] - (a-1)/[2(a^2 - 4)]

= (a+2)/(a-2)^2 - [a - 2 + a - 1]/[2(a+2)(a-2)]

= (a+2)/(a-2)^2 - [2a - 3]/[2(a+2)(a-2)]

= [2(a+2)^2 - (2a-3)(a-2)]/[2(a+2)(a-2)^2]

= [2a^2 + 8a + 8