# Thread: work out missing angle?

1. Hiandyboy,
Suggestions
1 Construct the given sided triangle. The x angle will be obtuse. By using th Pythagorean T solve for the segments on the 18 base created by the altitude on it
2 use simple trig to find the two acute angles which added will be the angle x

bjh

2. my calculator is in degrees mode.

3. would this work?

18^2= 10^2+11^2-2x10x11xcos?

324=100+121-220cos?

103=-220cos?

103/-220= -0.47

cos?=-0.47

?=inverse cos(-0.47)= 118.03??

4. Yep that works. Just tack on the units of degrees to your final answer, and you're done.

5. thanks alot!!! i hope we will do some more of these in calss, if not i will ask for some extra homework on them!

6. You're welcome. Have a good one!

7. Hi again andyboy,
What course are you taking? I assume its Trig or Advanced Math. You were having a lot of trouble so I explained a method that does not need the cosine rule for a 3 sided triangle. This method showed x= 117.9. It was a long way to Tipperary but you got there. The same result is obtained when you use -.468 for the value of cos x - 103/220

bjh

8. i am doing my GCSEs in maths

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