Question

I f an =n square -1 find s5 and s2

Answer 1

Step-by-step explanation:

An = n² - 1

A1 = a = 1² - 1 = 1 - 1 = 0

Sn = n/2 { a + An }

= n/2 { 0 + n² - 1 }

= n(n² - 1)/2

s5 = 5(5² - 1)/2

= 5 (25 - 1)/2

= 5 × 24/2

= 5 × 12 = 60

s2 = 2(2² - 1)/2

= 4 - 1

= 3