How do you solve #9d^2-81=0#?
You can factor out 9 immediately:
Or, you can plug the coefficients from the original equation into the quadratic formula. Remember this will solve any quadratic having of form
...substitute 'd's for x's, and use a = 9, b = 0, c = -81.
and plug 'em into the quadratic formula:
remember that coefficient b is zero for this case, so we get:
(I think the first way is easier, but hey.)