Question

for an AP second term is 12 and fourth term is 20 find the sum of fist 25 terms​

Answer 1

Hi mate

Here is ur answer

a2= 12
a+d=12

a=12-d.........(1)

a4=20
a+3d=20
12-d+3d=20....( from 1)
2d=8

➡️d=4

(1)..... a=12-d= 12-4

➡️a=8

s25 = n/2[2a+(n-1)d]

= 25/2[2(8)+(25-1)4]
=25/2[16+(24)4]
=25/2[16+96]
=25/2(112)
=25×56

➡️s25=1400

I hope this will help you....

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