Factor completely.

81-100x^2

Answer: (9+10x) (9-10x). Explanation: To factor this, look for numbers that can be FOILed (first, outer, inner, last). You know what if you separate the equation into two different parenthesis, one has to be negative and the other positive because there are no x^1 variables. 81 is equal to 9*9, and 100x^2 is equal to 10x*10x. Split these into two parenthesis, and add corresponding negatives. The answer should be (9+10x) (9-10x).