4x² - 8x - y² + 4y - 4 = 0
Factor the coefficient of x², which is 4, out of
the two x-terms
4(x² - 2x) - y² + 4y - 4 = 0
Factor the coefficient of y², which is -1, out of
the two y-terms
4(x² - 2x) - (y² - 4y) - 4 = 0
Get the term -4 off the left side by adding
4 to both sides:
4(x² - 2x) - (y² - 4y) = 4
Multiply the coefficient of x inside the parentheses,
which is -2 by ½ getting -1. Then square -1 getting +1.
Add +1 inside the first parentheses, and offset it by
adding +4 to the right side, since adding +1 inside
the first parentheses amounts to adding +4 to the left side
because of the 4 outside the first parentheses:
4(x² - 2x + 1) - (y² - 4y) = 4 + 4
Combine the 4 + 4 on the right as 8
4(x² - 2x + 1) - (y² - 4y) = 8
Multiply the coefficient of y inside the second parentheses,
which is -4 by ½ getting -2. Then square -2 getting +4.
Add +4 inside the second parentheses, and offset it by
adding -4 to the right side, since adding +4 inside
the second parentheses amounts to adding -4 to the left side
because of the - outside the second parentheses:
4(x² - 2x + 1) - (y² - 4y + 4) = 8 - 4
Combine the 8 - 4 on the right as 4
4(x² - 2x + 1) - (y² - 4y + 4) = 4
Factor x² - 2x + 1 as (x - 1)(x - 1) and then as (x - 1)²
Factor y² - 4y + 4 as (y - 2)(y - 2) and then as (y - 2)²
4(x - 1)² - (y - 2)² = 4
Next we must get a 1 on the right.
So we divide all the terms by 4
4(x - 1)² (y - 2)² 4
————————— - ———————— = ———
4 4 4
(x - 1)² (y - 2)²
————————— - ———————— = 1
1 4
Next we compare that to
(x - h)² (y - k)²
————————— - ———————— = 1
a² b²
which means that it is a hyperbolka that looks like this )(
We see that h = 1, k = 2, a² = 1 so a = 1 and b² = 4 so b = 2
The center = (h,k) = (1,2)
Plot the center (1,2)
Draw the transverse axis which is 2a or 2 units long and
is horizontal, with the center at its midpoint. That
means we draw 1 units left of the center and 1 units
right of the center to get the complete transverse
axis, drawn in green below:
Next draw the conjugate axis which is 2b or 4 units long and
is vertical, with the center at its midpoint. That
means we draw 2 units up from the center and 2 units
down from the center to get the complete transverse
axis, also drawn in green below:
Next we draw the defining rectangle, which is a
rectangle with the ends of the transverse and
conjugate axes as midpoints of the sides. I'll
draw it in green, too:
Next we draw the extended diagonals of the defining rectangle.
They will be the asymptotes of the hyperbola:
Now we can sketch in the hyperbola to have its vertices as
the ends of the transverse axis and to approach the \
asymptotes. I'll draw the hyperbola in red:
vertices, co-vertices, foci, and asymptotes
The vertices are the endpoints of the transverse axis.
They are (0,2) and (2,2)
The co-vertices are the endpoints of the conjugate axis.
They are (1,0) and (1,4)
To find the foci we calculate c from the formula
c² = a² + b²
c² = 1² + 2²
c² = 1 + 4
c² = 5_
c = √5
Then the foci are the points which are c units right
and left of the vertices. They are
_ _
(1+√5,2) and (1-√5,2)
I'll plot the two foci:
Now all we need are the equations of the two asymptotes:
The asymptote that slants uphill to the right passes through (0,0)
and (1,2),
We use the slope formula
Substitute in
y = 2x
That's the equation of the asymptote that slants
uphill to the right.
The asymptote that slants downhill to the right
passes through (2,0) and (1,2),
Using the slope formula
Substitute in
y = -2x + 2
That's the equation of the asymptote that slants
downhill to the right.
Edwin