Question 7809
1-125b^3
it is in the form of a^3 - b^3
for which the factorisation is (a-b)*(a^+ab+b^2)
here the value of a = 1
value of b = 5b
so that 
1-125b^3 = (1)^3 - (5b)^3 = (1-5b){1+(1*5b)+(5b)^2}
= (1-5b)(1+5b+25b^2) 
Ans