Question 166805
27a^3 - 64b^3 + 15a - 20b
;
Regroup
27a^3 + 15a - 64b^3 - 20b
:
factor out 3a and 4b
3a(9a^2 + 5) - 4b(16b^2 + 5); note the sign change when you factor out -4b