My attempt:

$$x'= -\sin\left(\frac{t}{1+t}\right) \* \frac{1}{(1+t)^2}$$

$$y'= \cos\left(\frac{t}{1+t}\right) \* \frac{1}{(1+t)^2}$$

then I attempted to divide y' on x' which resulted in

$$-\cot\left(\frac{t}{1+t}\right)$$

When I try to take the double dash of this it gives me 

$$\csc^2\left(\frac{t}{1+t}\right),$$

but this function is undefined at 0.