Question

need answer immediately for the 3rd one guys​

Answer 1

Answer:

1240

Step-by-step explanation:

We know that,

1² + 2² + .... + n² = [n(n + 1)(2n + 1)]/6

Now,

Given series is 1² + 2² + 3² + .... + 15²

Here, n = 15.

Replace n with 15 :

=> [15(15 + 1)(30 + 1)]/6

=> [15 * 16 * 31]/16

=> 1240

Hope it helps! mark as Brainliest if possible!