Question

15th term of AP 21,18,15​

Answer 1

Answer:

a+14d

21+14×-3

=-21

Step-by-step explanation:

Here is your answer for this question

Answer 2

EXPLANATION.

⇒ A.P. = 21, 18, 15,,,,,,

As we know that,

First term of an A.P. = a = 21.

Common difference of an A.P. = b - a = c - b.

Common difference of an A.P. = 18 - 21 = -3.

As we know that,

General term of an A.P.

⇒ Tₙ = a + (n - 1)d.

⇒ T₁₅ = a + (15 - 1)d.

⇒ T₁₅ = a + 14d.

Put the values in the equation, we get.

⇒ T₁₅ = 21 + 14(-3).

⇒ T₁₅ = 21 - 42.

⇒ T₁₅ = - 21.

                                                                                                                         

MORE INFORMATION.

(1) = Arithmetic progression (A.P.).

If a is the first term and d is the common difference then A.P. can be written as : a + (a + d) + (a + 2d) + (a + 3d) + ,,,,,

(2) = General term of an A.P.

Tₙ = a + (n - 1)d.

(3) = Sum of n terms in an A.P.

Sₙ = n/2[2a + (n - 1)d]  Or  Sₙ = n/2[a + Tₙ].

(a) = If sum of n terms Sₙ is given then general term Tₙ = Sₙ - Sₙ₋₁ where Sₙ₋₁ is sum of (n - 1) terms of an A.P.