Given below is the odd-number function. which of the following are equal to o(20)? check all that apply. o(n) = 2n - 1 a. o(19) + 1 b. the twentieth odd number c. 39 d. 19

The answer 
the only method for finding the answer is computing directly the value of O(20) by replacing n by  20, 
since we know that O(n) = 2n - 1
so, we get O(20) = 2*20 - 1 = 40-1=39
the answer is D. 19