The 4th term of an ap is 22 and 15th term is 66 find the first term and the common difference and the sum of series to 8 terms
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an=a+(n-1)d
22 = a +3d. (1)
66= a+ 14d. (2)
(i)-(2)->-44=-11d
d=4, Put in (I)
22=a+3d
22 = a +12
a=10
a=10,d=4,
sum of 8terms
Sn=n/2{2a+(n-1) d}
S8=8/2{2x10+ (8-1) 4}
= 4 (20+28) = 4x48=192
S8 =192. Ans
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