Answer:
a = 2
Explanation:
In an AP the difference between consecutive terms is common (equal), thus
t₂ - t₁ = t₃ - t₂ , that is
2a + 1 - (a + 1) = 4a - 1 - (2a + 1) ← distribute and simplify both sides
2a + 1 - a - 1 = 4a - 1 - 2a - 1
a = 2a - 2 ( subtract 2a from both sides )
- a = - 2 ( multiply both sides by - 1 )
a = 2