1.

If the nth term of an AP is (5n-3) find the sum of first 20 term of the AP using the formula​

Answer»

Given:- NTH term of ap=(5n-3)

Let's first take out the terms of the given ap.

So,

(5n-3)

For A1 put the VALUE of n as '1'.

a1=5(1)-3=2

For a2 put the value of n as'2'.

a2= 5(2)-3=7

Now for common difference we have,

d=a2-a1

=7-2=5

Now we know the formula sn=n/2[2a+d]

A/q,

S20=20/2[2×2+19×5]

S20=10(4+25)

S20=990

Thus,the sum is 990.


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