請估計下列函數的成長速率. (最好可以求出 big-Theta; 不然至少
分別求出 big-O 與 big-Omega; 再不濟用計算機也要猜出一個大概)

1. f(n) = n^2*log(n) + n*(log(n))^2
2. f(n) = 1*2 + 2*3 + 3*4 ... + n*(n+1)
3. f(n) = log((2n)!)

Ans: 
1. f(n) is in Theta(n^2*log(n))
2. f(n) is in Theta(n^3)
3. f(n) is in Theta(n log n)