How would I write the cosine law if I was trying to find theta given all sides?

Guest Oct 18, 2017

#1**+2 **

Let the sides be a, b and c

So we have that

a^2 = b^2 + c^2 - 2bc *cos (theta) rearrange as

2bc * cos(theta) = b^2 + c^2 - a^2 divide both sides by 2bc

cos (theta) = [ b^2 + c^2 - a^2 ] / [2bc ]

Take the cosine inverse

cos^{-1} ( [ b^2 + c^2 - a^2 ] / [2bc ] ) = theta

Remember that "theta" is the angle opposite side "a"

CPhill Oct 18, 2017