Question

In an Ap If the first term is 4 & the 9th
term is 28
, find the
the sum of
9 terms
​

Answer 1

Required Answer:-

Given:

• First term of the A.P. is 4.
• 9th term of the A.P. is 28.

To find:

• Sum of first 9 terms.

Answer:

• The sum of first 9 terms is 144.

Solution:

Given,

➡ First term (a) = 4

➡ 9th term = 28

Nth term of an A.P. is given by the formula,

Nth term = a + (n - 1)d

So,

➡ 9th term = a + (9 - 1)d

➡ a + 8d = 28

As the first term is 4. So,

➡ 4 + 8d = 28

➡ 8d = 28 - 4

➡ 8d = 24

➡ d = 24/8

➡ d = 3

Hence, common difference of the A.P. is 3.

Sum of first 9 terms of the A.P. is,

= 9/2[2 × 4 + (9 - 1) × 3]

= 9/2[8 + 24]

= 9/2 × 32

= 144

Hence, the sum of first 9 terms of the A.P. is 144. (Answer)

Learn More:

• Arithmetic Progression:- It is a sequence in which difference between two consecutive terms is same(constant) known as common difference.

Answer 2

Answer:

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