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In an AP Given d = 5, S9 = 75, find a and a9. - CBSE Class 10 - Mathematics

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Question

In an AP

Given d = 5, S9 = 75, find a and a9.

Solution

Given that, d = 5, S9 = 75

`S_n = n/2[2a+(n-1)d]`

`S_9 = 9/2[2a+(9-1)5]`

75=9/2(2a+40)

25 = 3(a + 20)

25 = 3a + 60

3a = 25 − 60

`a = (-35)/3`

an = a + (n − 1)d

a9 = a + (9 − 1) (5)

`= (-35)/3+8(5)`

`=(-35+120)/3=85/3`

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APPEARS IN

 NCERT Solution for Mathematics Textbook for Class 10 (2019 to Current)
Chapter 5: Arithmetic Progressions
Ex. 5.30 | Q: 3.05 | Page no. 112
Solution In an AP Given d = 5, S9 = 75, find a and a9. Concept: Sum of First n Terms of an AP.
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