Please find illustration attached
Answer and explanation:
I have illustrated the bisection of the lines using a diagram so it's easier to solve length of AB
Comparing line DE and CB, we know that DE is half of line DC and DC is half of CB, because CB= AC
Therefore DE is a quarter of line CB because length of DE × 4 will be equal to CB
To find length of AB, we go from known to unknown
We know from what we are given that line AB has a midpoint C, CB in line AB = 3x²+3x
CB=AC because CB is half of line AB
Therefore line AB
=3x²+3x+3x²+3x
= 6x²+6x