Question

hey friends plz answer the 2nd qn... given above...​

Answer 1

Step-by-step explanation:

Let first term be a and the common difference be d .

Now , 14 th term =twice the eighth term

→a+13d = 2(a+7d)

→a+13d=2a+14d

→-a= d

→d=-a .

Now ,

6 th term= -8

→a +5d = -8

→a-5a= -8 {d=-a}

→-4a=-8

→a= 2 .

Thus , d = -a= -2 .

Now , 20 th term= a+19d = 2 -38= -36 .

Thus sum of 20 terms

= n/2(a+ a+19d)

= 20 /2(2-36)

= 10×-34

= -340