Correct so expression= 4ab(25a^4-9b^2)= 4ab(5a^2-3b)(5a^2+3b)
You have the 2nd question correct
How do you factor when you have multiple variables?
100a5b - 36ab3
4 will factor into both 100 and 36. And ab will factor into both the variable parts?
m3 - 64 = (m-4)(m2+4m+16)
Is that correct?