Question

Find the sum of the first 40 terms of the arithmetic sequence 3/4,1/4,-1/4,-3/4,-5/4​

Answer 1

Answer:

Yeah this can be done using few formulas of arithmetic progressions

First of all

First term (a) = 3/4

Common difference (d) = -2/4 = -1/2

n = 40

Sum of an A.P = (2a + (n-1)d)/2

= (3*2/4 + (40-1)(-1/2))/2

=(3/2 - 39/2)/2

= (-36/2)/2

=-36/4

= -9

Thus sum of first 40 terms is -9

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