Question

Which is the equation of a hyperbola with directrices at x = ±3 and foci at (4, 0) and (−4, 0)?

Answer 1

Answer:

x^2/12 - y^2/4 = 1

Step-by-step explanation:

As the diretrices have simetrical values of x and have y = 0, the center is located at (0,0)

The formula for the diretrices is:

x1 = -a/e and x2 = a/e

And the foci is located at (a*e, 0) and (-a*e, 0)

So we have that:

a/e = 3

a*e = 4

From the first equation, we have a = 3e. Using this in the second equation, we have:

3e*e = 4

e^2 = 4/3

e = 1.1547

Now finding the value of a, we have:

a = 3*1.1547 = 3.4641

Now, as we have that b^2 = a^2*(e^2 - 1), we can find the value of b:

b^2 = 3.4641^2 * (1.1547^2 - 1) = 4

b = 2

So the equation of the hyperbola (with vertical diretrices and center in (0,0)) is:

x^2/a^2 - y^2/b^2  = 1

x^2/12 - y^2/4 = 1