3x a x 2 x b tell me the answer if you know it

Marya wants to factor the polynomial 36x^3 -22x^2 - 144x. which term can she add to the polynomial that would not change its grestest common factor? check all that apply

Each of the walls of a room with square dimensions has been built with two pieces of sheetrock, a smaller one and a larger one. the length of all the smaller ones is the same and is stored in the variable small. similarly, the length of all the larger ones is the same and is stored in the variable large. write a single expression whose value is the total area of this room. do not use any method invocations.

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?