15. The sum of the numbers from 1 to n can be computed as a. n(n+1)Y2 b. log n c. n(n-1)/2 d. n s algorithm can be used to find gcd(a,b). 16. a. eugenie euclid c. euripides d. euler can be used to find prime numbers. a. bouchard's algorithm b. mobius inversion the sieve of erastosthenes strassen's algorithm tries all possibilities to find the optimal solution. 18. A a. divide and conquer algorithm b. depth-first search c. binary search d. brute force algorithm 19. Which of the following represents the fastest growth rate? a. nlog n b. 2 c. n 20. The function fn) a. O(n) b. 0(n) c. O(n) d. O(n-1) n(n-1)/2 is 21. (5 points) What are the best case, worst case and average case efficiencies for sequential search algorithm? Give an explanation for your