# Math Help - Derivatives

1. ## Derivatives

I need to find the equation of the tangent line to the curve at the given value of t:
x=2cost
y=2sint
t=pi/3
Thanks for the help.

2. $\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}}$

3. Or, since the original curve is given in terms of the parameter t, write the tangent line in the same way:
$\frac{dx}{dt}= -2sin(t)$
$\frac{dy}{dt}= 2cos(t)$
so, at $t= t_0$, i.e. the point $(2cos(t_0), 2sin(t_0))$ the tangent line is given by $x= 2cos(t_0)- 2sin(t_0)(t- t_0)$, $y= 2sin(t_0)+ 2 cos(t_0)(t- t_0)$.

In particular, with $t= \pi/3$, $sin(\pi/3)= \sqrt{3}/2$ and $cos(\pi/3)= 1/2$ so the tangent line there is $x= 1- \sqrt{3}(t- \pi/3)$, $y= \sqrt{3}+ (t- \pi/3)$.