Area of Triangle Formed by Hyperbola Vertex Focus and Latus Rectum
Consider a branch of the hyperbola x2−2y2−22x−42y−6=0
with vertex at the point A. Let B be one of the end points of its latus rectum. If C is the focus of the hyperbola nearest to the point A, then the area of the triangle ABC is
To find the area of the triangle ABC, we first rewrite the equation of the given hyperbola in standard form:
x2−2y2−22x−42y−6=0
Group the x and y terms and complete the squares: (x2−22x)−2(y2+22y)=6 ((x−2)2−2)−2((y+2)2−2)=6 (x−2)2−2−2(y+2)2+4=6 (x−2)2−2(y+2)2=4
Dividing both sides by 4, we get the standard form of the hyperbola: 4(x−2)2−2(y+2)2=1
Let X=x−2 and Y=y+2. The equation becomes: a2X2−b2Y2=1
where: a2=4⟹a=2 b2=2⟹b=2
The eccentricity e of the hyperbola is: e=1+a2b2=1+42=23
In the (X,Y) coordinate system, the coordinates of the key points are:
Vertex (A): Lies on the transverse axis at (a,0)=(2,0).
Focus (C): The focus nearest to A is located at (ae,0)=(223,0).
Endpoint of Latus Rectum (B): The latus rectum passes through the focus C perpendicular to the transverse axis. Thus, B has coordinates (ae,ab2)=(223,1).
Since A and C both lie on the X-axis (Y=0), and B and C share the same X-coordinate (X=ae), the line segment BC is perpendicular to AC. Therefore, △ABC is a right-angled triangle with the right angle at C.
The length of the base AC is: AC=ae−a=a(e−1)=2(23−1)
The length of the height BC is: BC=ab2=22=1
The area of △ABC is given by: Area=21×base×height=21×AC×BC Area=21×2(23−1)×1=23−1