Mathematics
Show that the progression 11, 13, 15, 17, 19,……..is an A.P. Write down its :
(i) first term
(ii) common difference
(iii) 20th term.
AP
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Answer
Since, 13 - 11 = 2, 15 - 13 = 2, 17 - 15 = 2 and 19 - 17 = 2.
Hence, the series is an A.P. with common difference = 2.
We know that nth term of an A.P. is given by,
⇒ an = a + (n - 1)d, where a is the first term.
⇒ a20 = 11 + (20 - 1)2
= 11 + (19)2
= 11 + 38
= 49.
Hence, a = 11, d = 2 and a20 = 49.
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