The order of the terms in a sum doesn't matter. They can therefore be rearranged without changing the value. 3+6+1=6+1+32x+4x2+8=4x2+2x+8\begin{aligned} 3+6+1 &= 6+1+3\\ 2x+4x^2+8 &= 4x^2+2x+8 \end{aligned}3+6+12x+4x2+8=6+1+3=4x2+2x+8