Let the smallest term be x, and the largest term be 2x
Then AP formed= x, ?, ?, 2x
So,
sn = n/2[2a + (n - 1) d]
sn = n/2[a + (a + (n - 1)d)] = n/2
[From term + (last term)]
360°= 4/2 [x+ 2x]....[We know that → a+(n-1) d= last term= 2x]
⇒ 180°= 3x
⇒ x= 60°
Now, 60° is least angle.
= 60°= π/180° × 60°
⇒ 60° = π/3 rad