Question

Which expression is prime?
A) 2x2 - 72
B) 3x2 - 147
C) 7x2 - 112x
D) 6x2 + 7x + 3

Answer 1

\[2x^2-72=2(x^2-36)=2(x-6)(x+6)\]

see which are factorable and which isn't...

Answer 2

Yes, a prime expression cannot be factored any further.
If you can factor out anything (anything other than 1) then it is NOT prime.
The factor can be a constant (other than 1), an x, an x^2, etc. and if any such factor exists it is not a prime expression.