Answer:
Step-by-step explanation:
How can you remember the formula?
Well, it helps to know it's the Pythagoras Theorem with something extra so it works for all triangles:
Pythagoras Theorem:
(only for Right-Angled Triangles) a2 + b2 = c2
Law of Cosines:
(for all triangles) a2 + b2 − 2ab cos(C) = c2
So, to remember it:
think "abc": a2 + b2 = c2,
then a 2nd "abc": 2ab cos(C),
and put them together: a2 + b2 − 2ab cos(C) = c2
