Q26 of 180 Page 3

Find the 21st term of an AP whose first two terms are - 3 and 4.

First two terms of an AP are a = - 3 and a2 = 4.

As we know, nth term of an AP is


an = a + ( n - 1 )d


where a = first term


an is nth term


d is the common difference


a2 = a + d


4 = - 3 + d


d = 7


Common difference, d = 7


a21 = a + 20d


= - 3 + ( 20 )( 7 )


= 137


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