Find the partial sum

Question

Find the partial sum S10 for the arithmetic sequence with a=9,d=6

Answer 1

Hello Josh,

The formula for partial sum for arithmetic sequences is: S_n = (a₁ + a_n) * n/2

The formula for an arithmetic sequence is: a_n = a₁ + d*(n-1)

To apply the first formula, you need to know a₁₀, which you can use the 2nd formula to find.

a₁₀ = 9 + 6*(10-1) = 9 + 6*9 = 9 + 54 = 63

Now plug it in the first formula: S₁₀ = (9 + 63) * 10/2 = 72 * 10/2 = 72*5 = 360

Therefore, the partial sum S₁₀ = 360