Question

A geometric sequence has a4 = 4 and a5 = 7. What is a1 ? Your answer​

Answer 1

• 4⁴/7³ or 256/343

Explanation:

Given GP with

• a₄ = 4
• a₅ = 7
• a₁ = ?

Let the common difference is r, then

• a₅ = a₄r
• a₁r³ = 4
• a₁r⁴ = 7

Solve for r and then a₁:

• 4r = 7 ⇒ r = 7/4
• a₁(7/4)³ = 4
• a₁ = 4*(4/7)³ = 4⁴/7³ = 256/343