Why i cant apply the same method II from the following exercise (39)??

Carlos, in this case, x is less than 1. But this information can mean x is .5 (positive), or x can be -2 (a negative number that makes x and x+1 negative). In problem 39, we are told that x > 1, which means that x is always positive. Multiplying both by x+1 can either change or not change the greater or less than signs.