What are the directrices of the hyperbola given by the equation y^2/49 - x^2/9 = 1?

http://prntscr.com/k2979 - Here is a screenshot of the possible choices. I'm not sure if I chose the right one, can someone tell me.

Question

What are the directrices of the hyperbola given by the equation y^2/49 - x^2/9 = 1?

http://prntscr.com/k2979 - Here is a screenshot of the possible choices. I'm not sure if I chose the right one, can someone tell me.

jim_thompson5910 · Answer

you got it correct

jim_thompson5910 · Answer

oh wait, i have the axes flipped, one sec

jim_thompson5910 · Answer

ok I just confirmed and the distance from the center to the vertices is 7 units

so a = 7

the distance from the vertex to the focus is sqrt(58) units, so c = sqrt(58)

the formula for the directrix is 

d = a^2/c

d = (7^2)/sqrt(58)

d = 49*sqrt(58)/58

which is exactly what you have

So you are correct

anonymous · Answer

Thank you so much for your help!

jim_thompson5910 · Answer

np