Trigonometry

Sine rule:
$ \frac{a}{sinA}=\frac{b}{sinB}=\frac{c}{sinC} $
where a,b,c are the sides opposite to the angles A,B,C respectively.

Cos rule:
$ cosA=\frac{b^2 +c^2 -a^2 }{2bc} $
$ cosB=\frac{a^2 +c^2 -b^2 }{2ac} $
$ cosC=\frac{a^2 +b^2 -c^2 }{2ab} $

Projection formulae:
$ a=c cos B+bcosC $
$ b=a cos C+ccosA $
$ c=a cos B+bcosA $

Area of triangle:
$ area=\frac{1}{2} ac sinB=\frac{1}{2}ab sin C =\frac{1}{2} bc sin A $

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