you don't actually divide by 0. The concept of taking a limit is going towards 0, but you have to think you will never actually reach that number. How you need to think about it is that you're dividing 2+5 by a number extremely small. So the answer is infinity. Any number divided by something infinitely small will yield an extremely huge number. Hence as you approach 0, (2+5)/x^2 tends to infinity.