1/(1+y)(1-y) = 2/(1+y)^2 - 3/(1-y)^2
(1+y)(1-y)/(1+y)^2(1-y)^2 = 2(1-y)^2/(1-y)^2 - 3(1+y)^2/(1+y)^2(1-y)^2
去分母,得 1-y^2 = 2-4y+2y^2-3-6y-3y^2
解得 y = -1/5
1/(1+y)(1-y) = 2/(1+y)^2 - 3/(1-y)^2
(1+y)(1-y)/(1+y)^2(1-y)^2 = 2(1-y)^2/(1-y)^2 - 3(1+y)^2/(1+y)^2(1-y)^2
去分母,得 1-y^2 = 2-4y+2y^2-3-6y-3y^2
解得 y = -1/5