Originally Posted by

**MathBlaster47** I have an odd question, that I think I have worked out properly, but the answer makes no sense.

What are (a) the x-intercepts,(b) the y-intercepts and(c) the foci of the ellipse $\displaystyle \frac{x^2}{25}+ \frac{y^2}{36}=1$.

I have already determined that the x and y intercepts are: $\displaystyle \pm5$ and $\displaystyle \pm6$,respectively, meaning that the major axis is vertical as the y-intercept is greater than the x-intercept.

My problem is that when I use the relation:$\displaystyle c^2=a^2-b^2$

the result is -9, so c is the square root of -9--which doesn't exist and cant be graphed, meaning I did something wrong.....

What was it that I did wrong?