To simplify these expressions, we can use the binomial theorem.

For (a+b)^4-(a-b)^4, we can expand (a+b)^4 and (a-b)^4 using the binomial theorem.

(a+b)^4 = a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4
(a-b)^4 = a^4 - 4a^3b + 6a^2b^2 - 4ab^3 + b^4

Therefore, (a+b)^4-(a-b)^4 = (a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4) - (a^4 - 4a^3b + 6a^2b^2 - 4ab^3 + b^4)
= a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4 - a^4 + 4a^3b - 6a^2b^2 + 4ab^3 - b^4
= 8a^3b + 12a^2b^2

For (a+b)^3-(a-b)^3, we can expand (a+b)^3 and (a-b)^3 using the binomial theorem.

(a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3
(a-b)^3 = a^3 - 3a^2b + 3ab^2 - b^3

Therefore, (a+b)^3-(a-b)^3 = (a^3 + 3a^2b + 3ab^2 + b^3) - (a^3 - 3a^2b + 3ab^2 - b^3)
= a^3 + 3a^2b + 3ab^2 + b^3 - a^3 + 3a^2b - 3ab^2 + b^3
= 6a^2b + 6ab^2

So, (a+b)^4-(a-b)^4 = 8a^3b + 12a^2b^2
and (a+b)^3-(a-b)^3 = 6a^2b + 6ab^2.