Question

Find an A.P. whose 10th term is - 8 and 20th term is 12.​

Answer 1

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$10th \: term \: of \: AP= a + 9d = - 8...........(1) \\ 20th \: term \: of \: AP= a + 19d = 12...........(2) \\ \\ subtracting(1)from(2) \: we \: get \\ 10d = - 20 \\ d = - 2 \\ putting \: the \: value \: of \: d = - 2 \: in \: (1) \\ a - 18 = - 8 \\ \therefore \: a = 10 \\ so \: the \: AP \: will \: be \: 10 , 8 ,6 ,4....$