Give the common difference of the sequence 10, 9, 8, 7, ... (Note: the three dotes"..." mean the sequence of numbers does not end at the value 7, it keeps on going to infinity). Answer: Question 12 Not yet answered Marked out of 10.00 The closed formula for the partial sum 1+2+3+4+...++n is O a. n(n+1)/2 O b. n(n-1)/3 c. n(n+1)/3