plug in the value of x to evaluate the limit
limit does not exist
You need to evaluate the limit, hence, you need to replace `oo ` for x in equation:
Since ` ` you are subtracting a really, really big number from 9, the result on the inside of the square root will be negative. It is not possible to take the square root of a negative number (unless we involve the imaginary `i ` ).
the `lim_(x->oo)sqrt(9-x^2) ` does not exist.