Question

If a1= 5 and an = 2an-1 + 5 then find the value of a4.

Answer 1

a₄ = 75

Explanation:

using the recursive formula and a₁ = 5 , then

a₂ = 2a₁ + 5 = 2(5) + 5 = 10 + 5 = 15

a₃ = 2a₂ + 5 = 2(15) + 5 = 30 + 5 = 35

a₄ = 2a₃ + 5 = 2(35) + 5 = 70 + 5 = 75

Answer 2

`a_4=75`

Explanation:

Given:

• 
  `a_1=5`
• 
  `a_n=2(a_(n-1))+5`

`\implies a_2=2(a_1)+5=2(5)+5=15`

`\implies a_3=2(a_2)+5=2(15)+5=35`

`\implies a_4=2(a_3)+5=2(35)+5=75`