Question

which of the term of A.P :18,15,12.... is-6​

Answer 1

Answer:

the answer is 9th term and the above answer is wrong!

Step-by-step explanation:

an = a +(n-1)d

so an = -6, d=15 - 18 = -3, a = 18

-6 = 18 + (n - 1) -3

-6 - 18 = (n - 1) - 3

- 24 = (n - 1) -3

- 24/-3 = (n - 1)

8 = (n - 1)

8 + 1 = n

9 = n

therefore the -6th term is 9.

happy learning

Answer 2

9th term of the AP 18 , 15 , 12 , . . . . is - 6

Given :

The arithmetic progression 18 , 15 , 12 , . . . .

To find :

The term of the AP which is - 6

Concept :

If in an arithmetic progression

First term = a

Common difference = d

Then nth term of the AP

= a + ( n - 1 )d

Solution :

Step 1 of 3 :

Write down the given progression

Here the given arithmetic progression is

18 , 15 , 12 , . . . .

Step 2 of 3 :

Write down first term and common difference

The arithmetic progression is

18 , 15 , 12 , . . . .

First term = a = 18

Common Difference = d = 15 - 18 = - 3

Step 3 of 3 :

Find the term of the AP which is - 6

Let nth term of the AP which is - 6

Then nth term of the AP = - 6

a + ( n - 1 )d = - 6

⇒ 18 + ( n - 1 ) × ( - 3 ) = - 6

⇒ 18 - 3n + 3 = - 6

⇒ 21 - 3n = - 6

⇒ - 3n = - 27

⇒ n = 9

9th term of the AP 18 , 15 , 12 , . . . . is - 6

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