Question

If the 3rd and the 9th terms of an A.P. are 4 and − 8 respectively. Which term of this A.P. is zero.​

Answer 1

Answer refers in attachment.

It helps you.

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Additional information:-

FORMULAS OF AP:

1. Let a be the first term and d be the common difference of the AP. now, n term of the AP is given by

• $\large \underline{\boxed{\bold{\pink{\sf \: a_n = a + (n-1)d}}}} $

2. Let a be the first term and d be the common difference. Now, sum of first n terms of the AP is given by :

• $\large \underline{\boxed{\bold{\pink{\sf \: S_n= \frac{1}{2}[2 a+ (n-1)d]}}}} $

3. Let a be the first term and a, be the last term of the AP. now. S_n = (a + a_n)

• $\large \underline{\boxed{\bold{\pink{\sf \: S_n= \frac{n}{2} [ (a+a_n) ]}}}} $

4. Let S, be the sum of first n terms of AP. then sum of first (n-1) terms of the AP is S₁.

• $\large \underline{\boxed{\bold{\pink{\sf \:a_n=S_n-S_{a-1}}}}} $

5. If the number of terms in the AP is odd, then there will be only one middle^th term.

• $\red{\sf \: middle \: term =( \frac{n + 1}{2} ) term}$

If the number of terms in the AP is even, then there will be 2 middle terms.

• $\red{ \sf \: first \: middle \: term = ( \frac{n}{2} )^{th} term}$
• $\red{ \sf \: second \: middle \: term = ( \frac{n + 1}{2} )^{th} term}$

6. Let I be the last term and d be the common difference of AP.

Now, nth term from the end=

• $\large \underline{\boxed{\bold{\pink{\sf \:[l-(n-1)d] }}}}$

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