Trig!If b=4.3m, c=6.8m, and A=118°, find a
I don't know what to do with a "c" added to this. Our book only gives one example and it's nothing like this. Can anyone please help me on how to find side a?? D:

Question

Trig!If b=4.3m, c=6.8m, and A=118°, find a
I don't know what to do with a "c" added to this. Our book only gives one example and it's nothing like this. Can anyone please help me on how to find side a?? D:

anonymous · Answer

Actually no, there is not a picture provided. This was literally all the info given in this question :/

e.mccormick · Answer

So why not make one, just a rough sketch, not to scale.

e.mccormick · Answer

Does your book cover things like SSA, ASA, SAS, and so on?  A simple sketch can let you see which one this is.

anonymous · Answer

based on this, it looks like an SAS. But I am trying to look for the triangle sketches. It's only giving different formulas but I cannot find any that I could apply to this

e.mccormick · Answer

It is SAS.  What about the law of cosines and that unknown side?

anonymous · Answer

all I see is this, sinA/a=sinB/b 
but the side c in this question is what threw me off

e.mccormick · Answer

Well, there are no angles to the sides you knpow, so the law of sines can not yet be used.  That is why I said law of cosines.

e.mccormick · Answer

Three forms of the Law of Cosine (and there are more):$$a^2=b^2+c^2-2bc\cos(A) \
b^2=a^2+c^2-2ac\cos(B) \
c^2=a^2+b^2-2ab\cos(C)$$

e.mccormick · Answer

Which side do you NOT know.  That is the side you need to solve for.

anonymous · Answer

Ya sorry! I was writing down one of the laws in the book and I finally saw your response just now lol so I will use the law solving for a^2

e.mccormick · Answer

OK.  And you only need to remember one of them.  The others are just switching around letters.

e.mccormick · Answer

Here is the bad drawing I started with.  Obviously not to scale.
|dw:1367135906403:dw|
Now as I go, I fill in parts.