a2 = b 2 + c2 - 2bc cos A
Write down the formula
a 2 = b 2 + c 2 - 2bcCos A
Fill in the blanks
a 2 = 9.0 2 + 7.8 2 - 2(9.0)(7.8)cos 112
a 2 = 9.0 2 + 7.8 2 - 2(9.0)(7.8)cos 112
Finally answer the question
a 2 = 60.84 + 81 - -52.6
a 2 = 194.44
square root
a 2
square root
194.44
a = 13.9
Congratulations
you just learned how to find a side using Cosine Law
Now learn how to find an angle with cosine law
Change around the question switch the spots of a & c so that you are looking for c /cosC
c 2 = a 2 + b 2 -2abCos C
17.2 2 = 24.2 2 + 19.5 2 - 2(24.2)(19.5)cos C
Congratulations again
you finished your cosine law lesson :)
you finished your cosine law lesson :)