Question

Find two polynomials that have a sum of 4

Answer 1

There are infinitely many ways to do this. One such way is 
(x^2 + 10x + 4) plus (-x^2 - 10x)
note how the x^2 terms combine to 0x^2 or just 0. The same applies to the x terms as well. The only thing left is 4

So as you can see, the goal is to get everything to cancel but the 4. You can also have something like 
(2x^2-7x+2) plus (-2x^2 + 7x + 2)
and we have the same cancellations going on. This time we have 2+2 = 4 left over.