We are given two sides of a triangle that are 2 and 5 and the angle between them is pi/3 or 60 degrees. In this case, we can use the cosine law to relate the given dimensions and angle. The cosine rule goes c2 = a2 + b2 - 2abcos C; Substituting, c2 = 4 + 25 - 2*2*5*cos pi/3 ; c2 = 19; c = sqrt 19 = 4.36 units.
