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Question
The sequence −10, −6, −2, 2, ... is ______.
Options
an A.P., Reason d = −16
an A.P Reason d = 4
an A.P., Reason d = −4
is not an A.P.
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Solution
The sequence −10, −6, −2, 2, ... is an A.P. Reason d = 4.
Explanation:
The given sequence is –10, –6, –2, 2, ...
Here,
First term (a) = a1 = –1
Second term = a2 = –6
Third term = a3 = –2
Common difference (d) = a2 – a1
= –6 – (–10)
= 4
a3 – a2 = –2 – (–6)
= 4
Since, a2 – a1 = a3 – a2
Thus, the given sequence is an A.P.
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Q.5
Find the sum of natural numbers between 1 to 140, which are divisible by 4.
Activity: Natural numbers between 1 to 140 divisible by 4 are, 4, 8, 12, 16,......, 136
Here d = 4, therefore this sequence is an A.P.
a = 4, d = 4, tn = 136, Sn = ?
tn = a + (n – 1)d
`square` = 4 + (n – 1) × 4
`square` = (n – 1) × 4
n = `square`
Now,
Sn = `"n"/2["a" + "t"_"n"]`
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