Find the sum of first 20 terms of the arithmetic series in which 3rd term is 7 and 7th term is 2 more than three times its 3rd term.

740

Step-by-step explanation:

Let the AP be a, a+d, a+2d, a+3d, ...

The  term of AP is given by:

We are given that the third term is 7.

⇒  

⇒

Also, the seventh term is 2 more than three times the third term.

⇒

⇒

⇒

⇒

⇒

We can put it in (1)

⇒

⇒

⇒d=4

Now, the Sum of n terms of an AP is given by the formula:

So, Sum of first 20 terms would be:

⇒

⇒

⇒

⇒

Thus, The Sum of first 20 terms of the AP is 740.

w'x is 0.

hope it