in an A.P the first is 2 and sum of first five term is one-fourth of the next five next five terms. show that 20th term is. -112.
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a=2
S5=1/4(S10)
Hence, after solving,
5(S5)=S10
5( 5/2(2*2+4d)) = 5(4+9d)
10d + 10 = 9d + 4
Therefore, d= -6
a20 = a+19d
= 2+ 19(-6)
= 2-114
=-112
Hence proved.
S5=1/4(S10)
Hence, after solving,
5(S5)=S10
5( 5/2(2*2+4d)) = 5(4+9d)
10d + 10 = 9d + 4
Therefore, d= -6
a20 = a+19d
= 2+ 19(-6)
= 2-114
=-112
Hence proved.
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