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The 21st term of an AP whose first two t...

The 21st term of an AP whose first two terms are -3 and 4, is

A

17

B

137

C

143

D

-143

Text Solution

Verified by Experts

The correct Answer is:
B
Given, first two terms of an AP are a = -3 and a + d = 4.
`implies -3+d=4`
Common difference, `d=7`
` :. a_(21)=a+(21-1)d " " [ :' a_(n)=a+(n-1)d]`
` " " = -3+(20)7`
` " " =-3+140= 137`
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NCERT EXEMPLAR-ARITHMETIC PROGRESSIONS-Arithmetic Progressions
  1. The 11th term of an AP -5, (-5)/(2), 0, (5)/(2), …

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  2. The first four terms of an A.P. whose first term is -2 and the common ...

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  3. The 21st term of an AP whose first two terms are -3 and 4, is

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  4. If the 2nd term of an AP is 13 and 5th term is 25, what is its 7th ter...

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  5. Which term of an AP : 21, 42, 63, 84, … is 210 ?

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  6. If the common difference of an AP is 5, then what is a(18)-a(13) ?

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  7. What is the common difference of an AP in which a(18)-a(14)=32?

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  8. Two APs have the same common difference. The first term of one of the...

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  9. If 7 times the 7th term of an AP is equal to 11 times its 11th term, t...

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  10. The 4th term from the end of an AP -11, -8, -5, …, 49 is

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  11. The famous mathematician associated with finding the sum of the first ...

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  12. If the first term of an AP is -5 and the common difference is 2, then ...

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  13. The sum of first 16 terms of the AP 10, 6, 2, … is

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  14. In an AP, if a = 1, a(n)= 20 and S(n) = 399, then n is equal to

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  15. The sum of first five multiples of 3 is

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  16. Which of the following form of an AP ? Justify Your answer. (i) -1,-...

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  17. Justify whether it is true to say that -1, (-3)/(2), -2, (5)/(2), … ...

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  18. For the AP -3, -7, -11, … can we find directly a(30)-a(20) without ac...

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  19. Two A.P have the same common difference. The first term of one A.P is ...

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  20. Is 0 a term of the AP 31, 28, 25, …? Justify your answer.

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