Trigonometry

Submitted by alpha on Sun, 08/09/2009 - 11:53.

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