b

C, their diagonal corners are a respectively.

b

C, it's called relational expression.

a^2=b^2+c^2-2bc*cosa

b^2=c^2+a^2-2ac*cosb

c^2=a^2+b^2-2ab*cosc

Sine theorem: let three sides of a triangle be a.

b

C, their diagonal corners are a respectively.

b

C, and the radius of the circumscribed circle is r, then the relation a/sina=b/sinb=c/sinc is a sine theorem.