ANSWER : (9u - 8)2
STEPS:
Step-1 : Multiply the coefficient of the first term by the constant 81 • 64 = 5184
Step-2 : Find two factors of 5184 whose sum equals the coefficient of the middle term, which is -144 .
Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above, -72 and -72
81u2 - 72u - 72u - 64
Step-4 : Add up the first 2 terms, pulling out like factors :
9u • (9u-8)
Step-5 : Add up the four terms of step 4 :
(9u-8) • (9u-8)
Which is the desired factorization