As x goes to infinity the only term that matter is -5x^3. As x^3 goes to negative infinity what does is it's sign? If you can't picture it than try separating negative infinity into -1(∞). Then cube it: (-1(∞))^3 which becomes -1(∞)^3 because -1 cubed is still -1. Then what is infinity cubed? Still infinity right? So (-1(∞))^3 is negative infinity. However there's the coefficient to take into account. The negative coefficient will change negative infinity to infinity. So y goes to infinity as x goes to infinity.
