Question

Find the sum using the appropriate formula to the given term. 3 + 6 + 9 +... : S10​

Answer 1

`S_(10) = 135`

Explanation:

Given sequence is:

3 + 6 + 9 +...

Here,

a = 3, d = 6 - 3 = 3, n = 10

`\because S_n = (n)/(2) \{2a + (n - 1)d \} \\ \\ \therefore \: S_(10) = (10)/(2) \{2 * 3 + (10 - 1) * 3\} \\ \\\therefore \: S_(10) = 5 \{6 + 7 * 3\} \\ \\\therefore \: S_(10) = 5 \{6 + 21\} \\ \\\therefore \: S_(10) = 5 * 27 \\ \\ \huge \orange{ \boxed{\therefore \: S_(10) = 135}} \\ \\`