Question

(y-2)(y+2)(y^2+4)
Should I put the answer as y^4-16 or (y^2+4)(y^2-4)?

(x^3m-t^5n)^2
Answer: x^6m-t^10n

Answer 1

the simplified/preferred answer would be the one without the parenthesis

Make sure not to skip steps!
(x^3m-t^5n)^2

As you can see below, the 2nd and 3rd terms (both negative) do not cancel out! Also, watch your signs on the last term. Multipling two negative numbers gives you a positive number.

(x^3m)(x^3m) + second term:(x^3m)(-t^5n) + third term: (-t^5n)(x^3m) + last term:(-t^5n)(-t^5n)