Question

The sum of the first n terms of an AP is 5n-n2 . Find the nth term of is AP.

Answer 1

Sn = 5n - n²

° S1 = 5 × 1 - ( 1 )²

S1 = 5 - 1

S1 = 4

• a1 = S1

a1 = 4


° S2 = 5 × 2 - ( 2 )²

S2 = 10 - 4

S2 = 6

• a2 = S2 - S1

a2 = 6 - 4

a2 = 2


d ( common difference ) = a2 - a1

d = 2 - 4 = - 2


To find nth term ,

an = a + ( n - 1 )d

an = 4 + ( n - 1 ) ( - 2 )

an = 4 - 2n + 2

an = 6 - 2n

$an = 6 - 2n$

Answer 2

Answer:

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