Answer: Choice B
(x-1)(x^3+x^2+5x+6)
==========================================
Explanation:
The 1 in the upper left box means that x = 1 is a root of the original polynomial.
So this means x-1 is a factor of the original polynomial.
This is because x = 1 leads to x-1 = 0 after subtracting 1 from both sides.
-----------------
The 0 in the last position of the bottom row shows we got a remainder of 0.
Getting a remainder 0 tells us that (x-1) is a factor of the polynomial. This synthetic division table confirms our initial guess.
The other values in that bottom row (1, 1, 5, 6) form coefficients to the polynomial 1x^3+1x^2+5x+6, or simply x^3+x^2+5x+6
-------------------
So we know that (x-1) and (x^3+x^2+5x+6) are factors
Meaning that,
x^4+4x^2+x-6 = (x-1)(x^3+x^2+5x+6)
You can confirm this by expanding out the right hand side (distribution rule).
. Then replacing s with 4: