In an A.P the first term is 2 and the sum of the first five terms is one- fourth of the sum of the next- five terms.
Find common difference.
Find 20th term .
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given a=2 and S5=1/4×5/2{2×a6+(n-1)d} or 5/2{4+4d}=5/8{2(2+5d)+4d)) or 4(4+4d)=4+14d or. 16+16d=4+14d or d=-12/2=-6 so cd is -6. now a20= 2+19×(-6)=2-114 =-112 ...so 20th term is -112
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