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The 5th term & 12th term of anArithematic progression are 30 & 65 respectively.Find the sum of its 26th term . |
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Answer» given, a5=30 a12=65 s26=? a5=a+(n-1)d 30=a+(5-1)d 30=a+4d 30-4d=a --------(i) a12=a+(n-1)d substituting the value of a from (i), 65=30-4d+(12-1)d 65=30-4d+11d 65=30+7d 65-30=7d 35/7=d 5=d substituting the value of d in (i) 30-4(5)=a 30-20=a 10=a s26=n/2[2A+(n-1)d] =26/2[2×10+(26-1)5] =13(20+125) =13×145 =1885 |
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