In a triangle if a pair of angles is complementary, then the triangle is a right-angled triangle.
True
Consider a triangle ABC,
and Let A and C be a pair of angles for which they are complementary, which means ∠A +∠C = 90∘.
Thus ∠B = 90∘. (As, sum of angles of a triangle = 180∘)
Hence, the triangle is right angled triangle.