The greatest common factor of the terms 20a12b2 and -15a8b4 of the expression 20a12b2 - 15a8b4 is 5a8b2.20a12b2 = 5×4×a8×a4×b2 = 5a8×b2 × 4a4 and -15a8b4 = 5×-3×a8×b2×b2 = 5a8b2× -3b2
Hence, the expression 20a12b2 - 15a8b4 can be factorised as 5a8b2(4a4-3b2)​​