Any chance you can help me on this one mate?
lim t -> 4 (4-t)/(5-[sqrt t^2 + 9])
i subbed in x = 4 and solved and got 0. right?
You can also do the following:
$\displaystyle \lim_{t \to 4} \frac{4-t}{5-\sqrt{t^2+9}} = \lim_{t \to 4} \frac{(4-t)(5+\sqrt{t^2+9})}{(5-\sqrt{t^2+9})(5+\sqrt{t^2+9})}$
$\displaystyle =\lim_{t \to 4} \frac{(4-t)(5+\sqrt{t^2+9})}{25-(t^2+9)}$
$\displaystyle =\lim_{t \to 4} \frac{(4-t)(5+\sqrt{t^2+9})}{16-t^2}$
Proceed ...