The 21st term of an A.P. whose first two terms are -3 and 4 is
17
137
143
-143
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Given a = -3 and a2 = 4
We know that
an = a + (n - 1)d∴ a2 = -3 + (2 - 1) × d⇒ 4 = -3 + d⇒ d = 4 + 3⇒ d = 7.
a21 = -3 + (21 - 1) × 7⇒ a21 = -3 + 20 × 7⇒ a21 = -3 + 140⇒ a21 = 137.
Hence, Option 2 is the correct option.
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If the last term of A.P. 5, 3, 1, -1, …. is -41, then the A.P. consists of
46 terms
25 terms
24 terms
23 terms
If k - 1, k + 1 and 2k + 3 are in A.P. , then the value of k is
-2
0
2
4
If the first term of an A.P. is -5 and the common difference is 2, then the sum of its first 6 terms is
5
6
15