Question

How to derive sum of n terms of an A.P?

Answer 1

Answer:

Step-by-step explanation:

Sum = (n/2)(a+L)

n = number of terms

a = 1st term

L = last term

Answer 2

Sn = n² + 2n

we know,

Tn = Sn - Sn_1

= n² + 2n - (n -1)² -2(n -1)

= {n² - (n² -1)} + 2{ n - n +1 }

= 2n -1 +2

= 2n +1

so, Tn = 2n +1

then, A.P's are , 3 , 5 , 7, 9, 11 .......

20th term = 2(20) +1 = 41

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