Begin by using the cosine rule to find the unknown side.
Where a- unknown side, b is 12, c is 16 and angle in between is 108°
The cosine rule...
a² = b² + c² - 2bc cosA
= 12² + 16² - (2×12×16 cos108°)
= 518.655076
Taking the positive
square root...
a = 22.774
a = 22.8 cm nearest tenth
