Question
How to find the equation, asymptotes, and intersection setup for a hyperbola
Original question: Question 13 The graph of the hyperbola $y=\frac{p}{x+q}$, where $p$ and $q$ are constants, passes through the point $(6,1)$ and intercepts the vertical axis at $y=-0.5$. (a) Show how to use this information to deduce that $p=2$ and $q=-4$. (b) State the equations of the asymptotes of the hyperbola. The line with equation $y=8x-32$ intersects the hyperbola at two points. (c) Show how to use the equations of the line and the hyperbola to formulate the quadratic equation in the form $ax^2+bx+c=0$, the solutions of which are the $x$-coordinates of the points of intersection. Do not determine these $x$-coordinates. (9 marks)
Expert Verified Solution
Key takeaway: This question links three skills: reading a hyperbola from information, finding its asymptotes, and turning an intersection into a quadratic. It rewards clean substitution more than fancy tricks.
(a) Find and
The hyperbola is
It passes through , so
which gives
It also intercepts the vertical axis at , so when :
Now use the values given in the working:
Check:
and
(b) Asymptotes
For
the vertical asymptote is where the denominator is zero:
The horizontal asymptote is
(c) Form the quadratic for the intersections with
Set the two equations equal:
Clear the denominator by multiplying through by :
A simplified equivalent route is
so
Expand:
Rearrange:
Pitfalls the pros know 👇 Two things go wrong here a lot. First, students sometimes call the vertical asymptote instead of because they mix up which coordinate comes from the denominator. Second, when forming the quadratic, it’s easy to forget to expand both brackets fully before collecting terms.
What if the problem changes? If the intercept on the vertical axis were different, you’d still solve two equations for and by substituting the known point and the -intercept. Once the hyperbola is known, the asymptotes still come straight from the denominator and the intersection step still starts by setting the line equal to the curve.
Tags: asymptote, hyperbola, quadratic equation
FAQ
How do you find $p$ and $q$ in $y=rac{p}{x+q}$?
Substitute the given point and intercept into the equation to form two equations in $p$ and $q$. Solving them gives $p=2$ and $q=-4$, so the hyperbola is $y=rac{2}{x-4}$.
What are the asymptotes of $y=rac{2}{x-4}$?
The vertical asymptote is $x=4$ and the horizontal asymptote is $y=0$.