Question 29114
The problem should have been 4x^3y-20x^2y+16xy 

4x^3y-20x^2y+16xy 
=4xy(x^2-5x+4)
=4xy(x-4)(x-1)
Answer: 4xy(x-4)(x-1)

Explanation: Take out 4xy common
What is inside the bracket is a quadratic expression in x
And (x^2-5x+4)= x^2-4x-x+4  (splitting the term in x into two parts whose sum is the middle term and whose product if the product of the square term andthe constant term.
Product of the square term and the constant term
=(x^2)(4) = (1X2X2)x^2= (-4x)X(-x) 
and (-4x) +(-x) = -5x
(x^2-5x+4)
=x^2-4x-x+4  
=(x^2-4x)-x+4 
=x(x-4)-1(x-4) 
=xp-p where p = (x-4)
=p(x-1)
=(x-4)(x-1)