Question

Factoring quadratics

Answer 1

ax + bx = (a+b)x. This is known as the distributive property, multiplication distributes over addition.

Try picking concrete values for a, b and x to see that it works. It’s probably used at many other points in that video alone without you questioning it.

Answer 2

You're both right

(a+b)x is equivalent to ax+bx or bx+ax

He writes it that way so it matches the quadratics above, where there is only one x-term instead of two

Answer 3

Sal factored ax+bx into (a+b)x using a greatest common factor of x.