The Law of Cosines
February 25, 2010
Solving Oblique Triangles
Solving a triangle means finding the
lengths of all the sides and the measures
of all the angles.
This problem requires that we know three
of the sides or angles.
The Law of Sines
We use the Law of
Sines if we know:
• Two angles and any
side (AAS or ASA)
• One angle and two
sides, where one of
the sides is opposite
the known angle
(SSA)
Law of Cosines
We use the Law of
Cosines if we know:
• One angle and its two
adjacent sides (SAS)
• All three sides (SSS)
Questions
• What about AAA?
• On page 612, why are there “Alternative
Forms” of the Law of Cosines?
• Do we really need three equations for the
Law of Cosines?
Homework
Page 617, 1 – 7 (odd)