Who knows the sine and cosine theorem?

Sine theorem: The ratios of the lengths of the three sides of a triangle to the sine of the corresponding angles are all equal, and they are all equal to the diameter of the circumscribed circle.

That is: a/sinA=b/sinB=c/sinC=2R (R is the radius of the circumscribed circle of △ABC)

Cosine theorem:

a ^2 b^2-2*a*b*cosC=c^2

a^2 c^2-2*a*c*cosB=b^2

b ^2 c^2-2*b*c*cosA=a^2

It can be seen that the Pythagorean theorem is only a special case of the cosine theorem, that is, there is an angle, ∠A, ∠B Or the special case where ∠C is equal to 90 degrees.