Find y′′ in terms of x.
We can quickly solve this by realising that we can re-write the problem as y = 2x/(x2 - 1). By the quotient rule, we know that y'(x) will have a denominator equal to (x2 - 1)2 and we can also see that y''(x) will have a denominator equal to (x2 - 1)3. The only answer with this denominator is 4. Therefore the answer is:
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