What is the sum of the first 27 terms of the arithmetic sequence? −15,−11,−7,−3...
Difference between successive terms = +4
27th term = a1 + (n-1)(d)
-15 + (26)(4) = 89
Sn = n (a1+a27)/2 = 27 (-15+89)/2 = 999
Difference between successive terms = +4
27th term = a1 + (n-1)(d)
-15 + (26)(4) = 89
Sn = n (a1+a27)/2 = 27 (-15+89)/2 = 999