Question

If for an A.P first term a=6 and d=5 then find Sn and S10.

Answer 1

I hope it may be helpful...

Answer 2

Answer:

$a = 6 \\ d = 5 \\ \\ S_{n} = \frac{n}{2} ｛2a + (n - 1)d｝ \\S_{10} = \frac{10}{2} ｛2 \times 6 + (10 - 1)5｝ \\ S_{10} =5 ｛12 + (9)5｝ \\ S_{10} = 5｛12 + 45｝ \\ S_{10} = 5 \times 57 \\ S_{10} = \underline{ \underline{ 285}} \\ \\ S_{n} = \frac{n}{2} ｛2a + (n - 1)d｝ \\ S_{n} = \frac{n}{2} ｛2 \times 6 + (n - 1)5｝ \\ S_{n} = \frac{n}{2} ｛12 + (n - 1)5｝ \\ S_{n} = \frac{n}{2} ｛12 + 5n - 5｝ \\ S_{n} = \underline{ \underline{ \frac{n}{2} ｛ 5n + 7｝}}$