Find the HCF

Question

1) 7x and 9 : nothing
2) x^2(x-4) and x(x-4) : its (x-4)?
3) 6b and 2b^3 : 2b ,?
4) 6(x-1)^2 and 16(x-7)(x-1) : x-1 ,
5) 18y,27y, 9xy^2 : 9y
6) 5a^2 and 25a : 5a
7) 6abc, 8ab, 12bc : 2b
8) 9a^2b and 18ab^2 : 9ab

Answer 1

1) correct
2) x(x-4)
3) correct
4) 2(x-1)
5) correct
6) correct
7) correct
8) correct