Originally Posted by

**yoman360** here's the parametric equation:

x= tcos(t)

y= tsin(t)

for first derivative i get

dy/dx= $\displaystyle \frac {tcos(t)+sin(t)}{-tsin(t)+cos(t)}$

using:

$\displaystyle d^2y/dx^2$= $\displaystyle \frac{(d/dt)(dy/dt)}{dx/dt}$

this is what i get for the second derivative:

$\displaystyle d^2y/dx^2$= $\displaystyle \frac{-tsin(t)+2cos(t)}{-tsin(t)+cos(t)}$

but the answer in the back of the book is:

$\displaystyle d^2y/dx^2$= $\displaystyle \frac{t^2+2}{(cos(t)-tsint)^3}$

what did i do incorrectly or what am i doing incorrectly?