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Question
The 21st term of the AP whose first two terms are –3 and 4 is ______.
Options
17
137
143
–143
Solution
The 21st term of the AP whose first two terms are –3 and 4 is 137.
Explanation:
First two terms of an AP are a = – 3 and a2 = 4
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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