Question

The sum s of first n even natural numbers is given by the relation s=n(n+1)find n if the sum is 420

Answer 1

Answer:

20

Step-by-step explanation:

s = n(n+1)

given, the sum is 420

420 = n(n+1)

420 = n² + n

n² + n - 420 = 0

n² + 21n - 20n - 420 = 0

n(n+21) - 20(n+21) = 0\

(n+21) (n-20) = 0

n + 21 = 0

n = -21

n cannot be negative

so, n - 20 = 0

n = 20

HOPE IT HELPS YOU!