# Thread: work out missing angle?

1. -100 on each side, -121 on each side and +220 on each side so yo end up with 323=cos(?)

2. Too many steps at once. Try the -100 and -121 first. What equation do you get then?

3. 103=-220cos(?)

4. Correct. Now what is the -220 doing to the cosine?

5. im not too sure what it is doing

6. would you +220to (?) so it looks like 103=cos(220)?

7. No, no. It's multiplying the cosine. You have -220 times the cos(?). You would like to get rid of the -220, because it's preventing you from getting the cos(?) all on one side, with everything else on the other. So, how do you "reverse" multiplication?

8. times -220 by cos(?) ??

9. No, that's what you already have. Here's an analogy: solve 4 = 6x for x. What do you do?

10. 4/6=0.6
for my one i would do, 103/-220= 0.47?

11. Well, in the first case, you would probably write 0.67 instead of 0.6, but you have the right idea. Incidentally, because you are dividing a positive by a negative, the final result should be what: positive or negative?

12. nagative?

13. Correct. So your equation is now what?

14. 18^2= 10^2+11^2-2x10x11xcos?

324=100+121-220cos?

103=-220cos?

103/-220= -0.47

?=-0.47???

15. No. You have

cos(?) = -0.47.

Now you want to find the ?, but it's inside the argument of the cosine function. So how do you "undo" a cosine function?

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