If A is a factor of B then clearly dividing B by A will leave no remainder (or in other words a remainder of 0). For example, 3 is a factor of 12, so leaves no remainder (or a remainder of 0). This is the basic principle of the Factor Theorem which states that if dividing B by A leaves a remainder of 0, then A must by definition be a factor of B (eg leaves a remainder of 0, so therefore 5 has to be a factor of 25).
The Remainder Theorem finds the remainder, so if the remainder = 0, then the function dividing has to be a factor.
Eg is a factor of ?
Let,
as the remainder is 0, this implies that MUST be factor of