Question 443941
16x^2+56x+49   sub into {{{(a+b)^2=a^2+2ab+b^2}}}
(4x)^2+(2)*(4)*(7)+(7)^2
=(4x+7)^2

So therefore the square is (4x+7)*(4x+7).  So therefore one side of the square is 4x+7.
I'll try to make a sketch. (dots are filler)
...
....4x + 7
. . ____ ____
4x[16x^2[..28x..[
. .[____[____[
. .[ ..28x..[ ..49..[
+7[____[____[

Does that make sense?
That is supposed to be a square, divided into four sections.
Both sides are 4x+7.
If you add up the area inside, you'll get what was in the question.  I got the area in the subdivisions by l*w. 4x*4x=16x^2 ... 4x*7=28 ... 7*7=49