Question

the nth term of an APis given bu Tn=5-6n. find the sum of first n terms of the AP.

Answer 1

ap is -1 ,-7.......

so d is -6 so
s=n/2(-2+(n-1)×-6)
s=-4n-3n²

hope it helps you

Dear!

Answer 2

The nth term of the AP is 5-6n.

Let the first term be a.

common difference be d.

Hence:

nth term=a+(n-1)d

a+(n-1)d=5-6n

For the first term,n=1

first term is a.

a+0d=5-6*1

=a=5-6

=a=-1.

Now putting n=2

a+(2-1)d=5-6*2

=a+d=5-12

=a+d=-7

But a=-1

-1+d=-7

d=-6

a=-1 and d=-6.

Hence sum=n/2*[2a+(n-1)d]

=n/2*[-2+(n-1)(-6)]

=n/2[-2-6n+6]

=n/2[4-6n]

=n/2*2[2-3n]

=n[2-3n]

=2n-3n²

That's the answer.

Hope it helps.