I am unsure of the formula to answer this equation. Could someone give me a quick refresher. I do not want the answer, just the information necessary to find the answer myself. Thank you!
Hello : the sum is arithmetic secquence of common -diff is : (-7)-(-5) =(-5)-(-3) = (-3)-(-1) =-2 = d the first term is : a1 = -1 the formula of the sum : S= (n/2)(a1 +an) n is number of term an = a1+(n-1)d
