Answer:
Step 1 :Equation at the end of step 1
 ((81•(x4))-((72•(x2))•(y2)))+24y4
 Step 2 :
Equation at the end of step 2 :
 ((81 • (x4)) - ((23•32x2) • y2)) + 24y4
 Step 3 :
Equation at the end of step 3 :
 (34x4 - (23•32x2y2)) + 24y4
Step 4 :Trying to factor a multi variable polynomial
 4.1 Factoring 81x4 - 72x2y2 + 16y4 
Try to factor this multi-variable trinomial using trial and error 
 Found a factorization : (9x2 - 4y2)•(9x2 - 4y2)
Detecting a perfect square :
 4.2 81x4 -72x2y2 +16y4 is a perfect square 
 It factors into (9x2-4y2)•(9x2-4y2)
which is another way of writing (9x2-4y2)2
How to recognize a perfect square trinomial: 
 • It has three terms 
 • Two of its terms are perfect squares themselves 
 • The remaining term is twice the product of the square roots of the other two terms
Trying to factor as a Difference of Squares:
 4.3 Factoring: 9x2-4y2 
Put the exponent aside, try to factor 9x2-4y2 
Theory : A difference of two perfect squares, A2 - B2 can be factored into (A+B) • (A-B)
Proof : (A+B) • (A-B) =
 A2 - AB + BA - B2 =
 A2 - AB + AB - B2 =
 A2 - B2
Note : AB = BA is the commutative property of multiplication.
Note : - AB + AB equals zero and is therefore eliminated from the expression.
Check : 9 is the square of 3 
Check : 4 is the square of 2
Check : x2 is the square of x1 
Check : y2 is the square of y1 
Factorization is : (3x + 2y) • (3x - 2y) 
Raise to the exponent which was put aside
Factorization becomes : (3x + 2y)2 • (3x - 2y)2 
Final result :
 (3x + 2y)2 • (3x - 2y)2
Explanation: