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y = (x^2-1)/(x^2-3x-4) = (x-1)(x+1)/[(x+1)(x-4)]间断点 x = -1， x = 4lim(x-1)(x+1)/[(x+1)(x-4)] = lim(x-1)/(x-4) = 2/5,x = -1 是可去间断点；lim(x-1)(x+1)/[(x+1)(x-4)] = ∞，x = 4 是无穷间断点。
