x^2 - 81 = 0. Add 81 to each side.
x^2 = 81. Take the square root of each side.
x = 9, -9
The answer is the answer is C and F.
This is found by inserting the equation above into the quadratic formula or -b plus or minus the square root of b^2 - 4ac over 2a.
With that, you find that the first number is a -3, which eliminates choices B and D.
Then, solving the 4ac portion, you find that inside the square root the number is 29, which gives you the last two answer choices.
Hope this helps!
