You can use special product formula for this:
Square of a binomial:
(x-y)² = x² - 2xy + y²
Just substitute, simplify and let:
x = 2ab²
y = b
So we have:
(2ab² - b)² = (2ab²)² - 2(2ab²)(b) + b²
= 4a²b^4 - 2(2ab³) + b²
= 4a²b^4 - 4ab³ + b² ............ANSWER
