What is the multiplication rule of indices?

The multiplication rule is that when multiplying terms with indices, you add the indices up. In an example, if we had to simplify 3y² x 4y³ then we would first multiply the coefficients together (the numbers before the letters), 3x4 = 12. The next thing we do is multiply the y's, we have y² x y³, which means that our indices are going to come to 2+3 = 5. Therefore the answer is 12y⁵. Think of it this way: 2 x 2 is equal to 2². 2² x 2 is equal to 2 x 2 x 2, which is also equal to 2³. It is the exact same principle here, but we are using letters instead of numbers!