Question

5+9+13+17 sum of the 20terms of this AP is​

Answer 1

Step-by-step explanation:

Given: Sum of an AP=> 5+9+13+17+.......

Here, a=5

d=9-5=4.

n=20.

To find: S20=?

Formula of sum of n terms:

Sn=n/2(2a+(n-1)×d)

=>

S20=20/2(2×5+(20-1)×4)

=> 10(10+19×4)

=> 10(76+10)

=> 86×10

=> 860.

Answer 2

Answer:

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

sum of the 20terms= 20/2 [2×5 + (20-1)4]

= 10 [ 10 + 19×4 ]

= 10 [ 10 + 76 ]

= 10 × 86

= 860

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