Question

Please guys help me in this question

Answer 1

see it is on two pages
just check if it is right

Answer 2

Answer:

n = 20

Step-by-step explanation:

Even natural numbers are 2, 4, 6, ....

Hence, this is an AP with a = 2, d = 2

Given : Sn = 420

Also, Sn = [ n / 2 ] [ 2a + ( n - 1 ) d ]

Thus,

[ n / 2 ] [ 2a + ( n - 1 ) d ] = 420

[ n ] [ 2 ( 2 ) + ( n - 1 ) 2 ] = 840

n [ 4 + 2n - 2 ] = 840

n [ 2n + 2 ] = 840

2n [ n + 1 ] = 840

n [ n + 1 ] = 420

n ^2 + n - 420 = 0

n ^2 + 21 n - 20 n - 420 = 0

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

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

n = 20 or n = - 21

But, number of terms cannot be negative.

Hence, n = 20