Answer:
2.1
Step-by-step explanation:
using cosine theorem or substraction of two vector
b = AC = 5
c = AB = 6
a² = b² + c² - 2bc cos A
a² = 5² + 6² - 2*5*6 cos 20°
a² = 4.62
a = √4.62
a = 2.149
a ≈ 2.1
