Rewrite a4 as (a2)2.
Let u=a2. Substitute u for all occurrences of a2.
Factor by grouping.
For a polynomial of the form ax2+bx+c, rewrite the middle term as a sum of two terms whose product is a⋅c=4⋅28=112 and whose sum is b=23.
Factor 23 out of 23u.
Rewrite 23 as 7 plus 16
Apply the distributive property.
Factor out the greatest common factor from each group.
Group the first two terms and the last two terms.
Factor out the greatest common factor (GCF) from each group.
Factor the polynomial by factoring out the greatest common factor, 4u+7.
Replace all occurrences of u with a2.