Help!! I have a question for limit negative infinity why it change minus to plus

You don't have to change to +inf. It simply means that 1/x, 2/x, 4/x become infinity small negative numbers which still approach 0 from the left. 5/x^2 ---> 0 from the right. The x's in the numerator still cancel out as 2 negatives. All is good. The limit is still 2.