Question

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

Answer 1

Answer:

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S=3+4+8+9+13+14+18+19+....40 terms

=7+17+27+37+...20 terms

it is in A.P

∴s=

2

20

[2×7+(20−1)10]

=10(14+190)

=10×204

=20×102

as s=(102)m

⇒20×102=102×m

m=20