<span>x intercept when f(x) = 0
so
</span><span>x^2-81 = 0
x^2 = 81
x = + 9 and x = -9
Answer
</span><span>C -9</span>
I think -6 switches to -3
Mathematics is math, geometry, algebra, calculus
Your question seems a bit incomplete, but for starters you can write

Expanding where necessary, recalling that

, you have

and you can stop there, or continue to rewrite in terms of the reciprocal functions,

Now, since

, the final form could also take

or