Question

find the sum of first 25 terms of AP whose nth term is 1-4n

Answer 1

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Answer 2

To find first term put 1 in n

So a =-3

Find second term by putting 2 in n So second term is -7

On subtracting -3 from -7 you get the difference for AP I.e. -4

To find the sum of first 25 terms use the formula

Sn=n/2(2a+(n-1)d)

25/2(-3*2+24*-4)

= -1250