# Hi, need some help with tangents and asymptotes

• Feb 4th 2013, 08:45 AM
jezb5
Hi, need some help with tangents and asymptotes
Hi all, I've recently bought a few maths books to study in my spare time and I'm stuck on the below question. I've found the point P and I think the equation of the tangent is y = (4rt3)(x) - 2rt3. I have no idea how to find the equations of the asymptotes.

This question is about a Hyperbola in R^2.

It is described by the below parametric equations.

x = sec t, y = 2 tan t (t ∈ (-π/2 , π/2) U ( π/2 , (3π)/2)

The coordinates of point P, where t = π/3, are ( 2 , 2*sqrt3)

The gradient of the tangent to the hyperbola at the point with parameter t is 2/sin t, where t is not equal to 0 or π. Using this information, ﬁnd the equation of the tangent to the hyperbola at the
point P.

Find the equations of the asymptotes of the hyperbola

So could someone please confirm my answer, for the equation of the tangent and how to get the equations of the asymptotes?

Thanks
(Talking)
• Feb 4th 2013, 12:19 PM
johng
Re: Hi, need some help with tangents and asymptotes
I think you dropped a 3 in your calculation (or in your typing of your answer). The equation of the tangent line is:
$3y=4\sqrt{3}x-2\sqrt{3}$

Now as to the asymptotes: Remember, $1+tan^2(t)=sec^2(t)$, so your hyperbola in standard form is ${x^2\over 1}-{y^2\over 4}=1$ and so the asymptotes are $y=\pm 2x$.

Alternatively, the asymptotes for such a hyperbola are of the form $y=\pm mx$ where m= $\lim_{x\rightarrow \infty}{y\over x}$. Parametrically, ${y\over x}=2sin(t)$ and for x to go to infinity, t must approach $\pi/2$. So $m=\lim_{t\rightarrow \pi/2}2sin(t)=2$.
• Feb 5th 2013, 05:13 AM
jezb5
Re: Hi, need some help with tangents and asymptotes
Thanks for the help Johng, it always seems so much clearer when you have the answer :D