The sum of first n terms of an AP is 13n2 - 21n , find its 10th term.a

1.	The sum of first n terms of an AP is 13n2 - 21n , find its 10th term.anybody help pls!
Answer» Step-by-step EXPLANATION: Sn=1/2(3n^2+7n) S1=1/2(3+7)=5 S2=1/2(34+72)=26/2=13 We KNOW S1=a1=5 S2=a1+a2=13 S2-s1=a1+a2-a1 13-5=a2 a2=8 We know d=a2-a1 d=8-5=3 nth term of AP =an=5+(n-1)3 an= 2+3n Therefore 20th term = a20= 2+3(20)=62 Hence 20th term of AP is 62

The sum of first n terms of an AP is 13n2 - 21n , find its 10th term.anybody help pls!

Answer»

Step-by-step EXPLANATION:

Sn=1/2(3n^2+7n)

S1=1/2(3+7)=5

S2=1/2(3*4+7*2)=26/2=13

We KNOW

S1=a1=5

S2=a1+a2=13

S2-s1=a1+a2-a1

13-5=a2

a2=8

We know d=a2-a1

d=8-5=3

nth term of AP =an=5+(n-1)3

an= 2+3n

Therefore 20th term =

a20= 2+3(20)=62

Hence 20th term of AP is 62

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The sum of first n terms of an AP is 13n2 - 21n , find its 10th term.anybody help pls!​

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The sum of first n terms of an AP is 13n2 - 21n , find its 10th term.anybody help pls!