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If nth term of A.P. is (2n+1), what is the sum of its first three terms ? |
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Answer» Lakin mera ta 15 aya hai Nth term =2n+1Now put n=1 2*1+1=3 ..............1Now put n=2 2*2+1=5 ..............2From 1 and 2 we have a=3D=5-3=2Using formula Sn=n/2(2a+(n-1)d) Sn=3/2(2×2+(3-1)*2) Sn=3/2(4+4) Sn=3/2*8 Sn=3*4 Sn =12 The required Sn is 12 15 |
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