Question

which term of the series 12+9+6+..... is equal to -30​

Answer 1

Answer:

15 term

Step-by-step explanation:

an=a+(n-1)d

-30=12+(n-1)-3

-30-12=(n-1)-3

-42=(-3n+3n)

-42-3=3n

45=3n

n=15

Answer 2

15th term of the series 12 + 9 + 6 + . . . . . is equal to - 30

Given :

The series 12 + 9 + 6 + . . . . .

To find :

Which term of the series 12 + 9 + 6 + . . . . . is equal to - 30

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 series

Here the given series is

12 + 9 + 6 + . . . . .

Step 2 of 3 :

Write down first term and common difference

The given series is an arithmetic progression

First term = a = 12

Common Difference = d = 9 - 12 = - 3

Step 3 of 3 :

Find which term of the series is equal to - 30

Let nth term of the series is equal to - 30

Then nth term of the AP = - 30

a + ( n - 1 )d = - 30

⇒ 12 + ( n - 1 ) × ( - 3 ) = - 30

⇒ 12 - 3n + 3 = - 30

⇒ 15 - 3n = - 30

⇒ - 3n = - 45

⇒ n = 15

15th term of the series 12 + 9 + 6 + . . . . . is equal to - 30

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