I had this equation
x² = a² + b² - c²
these figures fit the equation
a=10, b=5, c=2 giving x=11
121 = 100 + 25 - 4
then it occured to me that the original equation looked very like the Cosine Rule
c² = a² + b² - 2ab Cos(c)
2ab Cos(c) = a² + b² - c²
so combining this with my original equation I would have thought
x² = 2ab Cos(c) which it doesn't ¿ 2 x 10 x 5 x Cos(2) = 99.94......
what did I miss or misunderstand?