How do you factor completely n^4 + 2n^2w^2+ w^4n4+2n2w2+w4?

1 Answer
Jan 2, 2016

n^4+2n^2w^2+w^4n4+2n2w2+w4

=(n^2+w^2)^2=(n2+w2)2

=(n-iw)^2(n+iw)^2=(niw)2(n+iw)2

Explanation:

n^4+2n^2w^2+w^4n4+2n2w2+w4

=(n^2)^2+2(n^2)(w^2)+(w^2)^2=(n2)2+2(n2)(w2)+(w2)2

=(n^2+w^2)^2=(n2+w2)2

In addition, if we allow Complex coefficients then n^2+w^2n2+w2 can be treated as a difference (!) of squares, being of the form a^2-b^2a2b2 with a=na=n and b=iwb=iw.

The difference of squares identity can be written:

a^2-b^2 = (a-b)(a+b)a2b2=(ab)(a+b)

So we find:

n^2+w^2 = n^2 - (iw)^2 = (n-iw)(n+iw)n2+w2=n2(iw)2=(niw)(n+iw)

Hence we can write:

n^4+2n^2w^2+w^4 = (n-iw)^2(n+iw)^2n4+2n2w2+w4=(niw)2(n+iw)2