Answer:
[tex]2abCosC = 1[/tex]
Step-by-step explanation:
The cosine rule is
=> [tex]a^2= b^2+c^2-2abCosC[/tex]
For 2abCosC, it becomes
=> [tex]2abCosC = b^2+c^2-a^2[/tex]
=> [tex]2abCosC = (2)^2+(1)^2-(2)^2[/tex]
=> [tex]2abCosC = 1[/tex]
