Hey Gang:

I have my final exam tomorrow night and I have "preparation test" I was given, so I have been finding like example questions to quiz myself - here are my weakspots that I can quite get, as there are no samples in all of my textbooks that the same "type":

1. State the sum of focal radii for the ellipse with the equation:

$\displaystyle \frac{x^2}{16}+\frac{y^2}{9}=1$

I get 2 different answers via this:

$\displaystyle a^2=16$, therefore, a=4

$\displaystyle b^2=9$, therefore, b=3

$\displaystyle c^2=a^2+b^2$

$\displaystyle c^2=16+9$

$\displaystyle c^2=25$, therefore c=5, therefore the foci=5, therefore sum of focal radii=10

OR, according to my book, sum of focal radii=2a, therfore 2(4)=8?

2. State the equation of the directrix for the parabola with the vertex (0,0) and focus (0, -3).

$\displaystyle x^2=4py$

$\displaystyle x^2=4(-3)$

3. Solve for x: $\displaystyle 3+9^{1-2x}$

I have NO idea how to approach this one. I have never seen a variable *in* an exponent. A hint or two, please on how to start? (I am probably just mental-blocking, so a push in the right direction will most likely make me go "AHH!")

Thanks for all & any help!