Hi guys I'm having trouble understanding this concept on problems like these

1. Lim CosX / 1 - Sinx

x->(pi/2)+

the answer would be Negative Infinity

2. Lim e^x - 1 / x^3

x->0

the answer would be Infinity

My question is why would the answers be infinity or negative infinity. I have no clue what is going on. Any detailed, step by step help would be greatly appreciated. Thanks