Confused in how to insert a slack variable in a constrain inequality

According to my understanding , we should put a slack variable to equate an inequality constrain by inserting the slack varaible in the side that is less than the other side , for example if we have 4x+2<2 this will be 4x+2+slack_variable=2 .But here in Wikipedia : In the example section , it says the following “By introducing the slack variable y>=0, the inequality Ax<=b can be converted to the equation y-Ax+b = 0” Which means that the slack variable is inserted in the bigger side ! Please some one explain this confusion.