∠2 and ∠3
1) Given that ∠1 is an external angle, then we can say that his measure is given by the sum of two non-adjacent interior angles. According to the Exterior Angle Theorem.
2) So we can write:
m∠1 = m∠2 + m∠3
3) Therefore we can say that the remote interior angles of ∠1 are ∠2 and ∠3