Question

How do you add and subtract indices?

Answer 1

Https://m.youtube.com/watch?v=PLME8ZRKMWU

Answer 2

When adding or subtracting with powers, the terms that combine always have exactly the same variables with exactly the same powers. Because the variables are the same (x) and the powers are the same (there are no exponents, so the exponents must be 1), you can add the variables.