## anonymous one year ago Fan & Medal to most helped Calculate EBA , given DA and m EFA =178º. The figure is not drawn to scale 90° 45° 133° 266° http://static.k12.com/eli/bb/817/-1/0/2_36869_44974/-1/5c45df68fdad740c9f94d22ea5f92dd60c7a03f7/media/ccdbc5a3efc5b98917c43109efe2d5434ef545be/mediaasset_651869_1.jpg

1. dan815

oh these are interesting

2. dan815

have u tried anything

3. dan815

|dw:1438749327954:dw|

4. anonymous

i thoguht it wa 90.......

5. anonymous

but now i think it is 45

6. dan815

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7. dan815

u know that triangle there has a 91, so that angle has to be less than 89 at least

8. DanJS

This page i linked before is a good help... http://www.regentsprep.org/Regents/math/geometry/GP15/CircleAngles.htm

9. DanJS

very bottom one this time

10. anonymous

so it is 90?

11. mathstudent55

@HWBUSTER00 The problem states "given DA", but the measure of arc DA is not there. What is it?

12. mathstudent55

|dw:1438787940138:dw|

13. mathstudent55

Without the measure of arc AD, you can;t solve this problem.

14. anonymous

...well there are multiple choice so it is one of them

15. mathstudent55

Why does the problem state "given DA" when DA is not given above? Did you copy all the information from the problem into your post?

16. anonymous

lol yes i did . that is the exact question . i think the teacher messed up . but that is the question

17. mathstudent55

Well, then, let's see if there are choices we can eliminate. |dw:1438788488246:dw|

18. mathstudent55

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19. mathstudent55

Now let's look at the choices. Choice A. m<B = 90 2(90) = 178 - mDA mDA = -2 Since an arc cannot have a negative measure, choice A can't be correct.

20. mathstudent55

Choice B. m<B = 45 2(45) = 178 - mDA mDA = 88 This solution is possible, since we get a positive number for mDA

21. anonymous

so since it is less than 90 it has to be 45 right

22. mathstudent55

Choice C. m<B = 133 2(133) = 178 - mDA mDA = -88 This solution is not possible, since we get a negative number for mDA

23. mathstudent55

Choice C. m<B = 266 2(266) = 178 - mDA mDA = -354 This solution is not possible, since we get a negative number for mDA

24. anonymous

so it is 45

25. mathstudent55

The only solution that works is B. 45

26. mathstudent55

yes

27. anonymous

thanks also what is cos(x) when it is -1

28. anonymous

is it 360 or -360

29. mathstudent55

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30. mathstudent55

The angle whose cosine is -1 is 180 or -180, and all coterminal angles.

31. anonymous

oh so nothing it is not 360 or -360. ok thats all i needed to know

32. mathstudent55

360 and -360 is the same as 0 degrees. There, the cosine is 1, not -1

33. anonymous

ok thank you

34. mathstudent55

You're welcome.