Question

Evaluate a20 and write what it represent in an=4n-1 sequence

Answer 1

Answer:

$a20 = 79$

Step-by-step explanation:

$a20 = 4 \times 20 - 1 \\ a20 = 80 - 1 \\ a20 = 79$

It represents the 20th term of the sequence

Answer 2

The 20th term, a₂₀ = 79

Given:

The algebraic expression of a sequence is  $a_{n}$ =4n-1  

To find:

Evaluate a₂₀ and write what it represent in $a_{n}$ =4n-1  sequence

Solution:

Given The algebraic expression of a sequence is  $a_{n}$ =4n-1  

To find a₂₀ substitute n = 20 in given algebraic expression

Then a₂₀ = 4(20) - 1 = 80 - 1 = 79

Therefore, a₂₀ = 79

                           (or)

Take n = 1 ⇒ a₁ =4n-1 = 4(1) - 1 = 3

Take n = 2 ⇒ a₂ =4n-1 = 4(2) - 1 = 8 - 1 = 7

Common difference d = a₂ - a₁ = 7 - 3 = 4  

As we know nth term = a + (n-1)d

                  20th term = 3 + (19)(2) = 3 + 76 = 79

Therefore, a₂₀ = 79  

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