Answer:
d = 10.5, a₁ = - 3.5
Step-by-step explanation:
The n th term of an AP is
= a₁ + (n - 1)d
where a₁ is the first term and d the common difference
Given a₂ = 7 and a₄ = 28 , then
a₁ + d = 7 → (1)
a₁ + 3d = 28 → (2)
Subtract (1) from (2) term by term to eliminate a₁
2d = 21 ( divide both sides by 2 )
d = 10.5 ← common difference
Substitute d = 10.5 into (1)
a₁ + 10.5 = 7 ( subtract 10.5 from both sides )
a₁ = - 3.5 ← first term