(a) Given, the ratio of angles of a triangle is 5 : 3 : 7. Let angles of a triangle be ∠A,∠B and ∠C. Then, ∠A = 5x, ∠B = 3x and ∠C = 7x In ΔABC, ∠A + ∠B + ∠C = 180° [since, sum of all angles of a triangle is 180°] 5x + 3x + 7x = 180° ⇒ 15x = 180° x = 180°/15= 12° ∠A = 5x = 5 x 12° = 60° ∠B = 3x= 3 x 12°= 36° and ∠C =7x = 7 x 12° = 84° Since, all angles are less than 90°, hence the triangle is an acute angled triangle