Question

Find the sum of series 1+2+3+...n=666

Answer 1

Step-by-step explanation:

S(n) = n(n+1)/2

666*2 = n(n+1)

n² + n - 1332 = 0

n²+37n-36n - 1332 = 0

n(n+37) -36(n+37) = 0

(n+37)(n-36) = 0

n = 36 ✓

So , S(36) = 666