Maybe im doing this wrong, but this doesn't seem to exist, or the answer is undefined.

Find an equation for the line tangent to the curve at the point defined by the given value of t. Also, find the value of $\displaystyle d^2y/dx^2$ at this point.

$\displaystyle x= -cos t $

$\displaystyle y= 7+sin t $

$\displaystyle t= pi/2$

Well, I did $\displaystyle -cos(pi/2) = 0$

and $\displaystyle 7+sin(pi/2) = 8$

$\displaystyle dx/dt = sin(pi/2) = 1$

$\displaystyle dy/dt = cos(pi/2) = 0$

$\displaystyle dy/dx= cos t / sin t $ or $\displaystyle dy/dx = cos t$

so, I plugged back in the $\displaystyle pi/2$ to get $\displaystyle cot(pi/2) = UND$

So I checked in my calculator, and the oval does not even go through the point $\displaystyle pi/2$, so it cant exist? Did I do something wrong?