Find the coordinates of the foci of the hyperbola y^2/9-x^2/16=1.
A) (4, 0) and (-4, 0)
B) (5, 0) and (-5, 0)
C) (0, square root 7) and (0, -square root 7)
D) (0, 5) and (0, -5)

Question

Find the coordinates of the foci of the hyperbola y^2/9-x^2/16=1.
A) (4, 0) and (-4, 0) 
B) (5, 0) and (-5, 0) 
C) (0, square root 7) and  (0, -square root 7)
D) (0, 5) and (0, -5)

anonymous · Answer

-9=-16+c^2
so c^2=7
c=sqrt7  or c=-sqrt7
so answer must be C.

directrix · Answer

I did not get C as the correct option. Perhaps I made an error.

anonymous · Answer

definetely you made an error :)

directrix · Answer

a^2 = 9 and b^2 = 16

c^2 - a^2 = b^2
c^2 = 9 + 16
c^2 = 25
c = +5 or -5

Foci at (0, -5) and (0, 5).

maddss · Answer

So what's the answer?

goformit100 · Answer

C) (0, square root 7) and (0, -square root 7)|dw:1364174979339:dw|

maddss · Answer

thanks
:)

directrix · Answer

@maddss Take a look at the graph and the statement of the foci given and see what you think. http://www.wolframalpha.com/input/?i=y%5E2%2F9+-+x%5E2%2F16+%3D+1+foci

anonymous · Answer

@marsss is wrong. 16+9=25, sqrt of 25 is 5, and the graph is up and down, so the foci would be (0,5)(0,-5)