Solve the triangle in which a = 2 cm, b = 1 cm and c = cm.

In a ∆ABC, if , show that the triangle is isosceles.

In a ∆ABC, if , show that the triangle is right-angled.

In a ΔABC, if a = 3 cm, b = 5 cm and c = 7 cm, find cos A, cos B, cos C.

If the angles of a triangle are in the ratio 1 : 2 : 3, prove that its corresponding sides are in the ratio .