# Cosine Rule and 3D-Trig... help!Watch

Thread starter 3 years ago
#1
Okay so firstly I'm stuck with cosine rule. It's an A* question and I have tried to look for ways to find the answer but I can't.Attachment 492803492805

Then 3D Trig is the same, A*, tried my best but failed.

Can anyone help me with the two questions? Any help will be appreciated, thanks!

EDIT: The 2nd one down is the cosine rule, the 1st one is trig. Sorry! It wouldn't let me place it properly!
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3 years ago
#2
For the first question FC can be found with simple trig by using triangle ABE. (EB = FC). CA can be found with Pythagoras - we know both of the other sides. Then Pythagoras can be used to find AF.
Number 2, use area=1/2absinC. Simple trig (sohcahtoa) will get you the sides you need, or you could use the sine rule. Hope this can get you started! Feel free to post answers, I'll check them or any further questions.
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