## berrypicking 2 years ago solve equation in the interval from 0 to 2pi. 7 cos 2t =3

1. berrypicking

corrections 7 cos 2t=3

2. cwrw238

arccos 3/7 - your calculator will give u the value of t in first quadrant the other value is in 4th quadrant

3. berrypicking

what does arccos mean

4. berrypicking

am I setting calculator in rad. or degrees

5. cwrw238

oh - then find angle whose cos is 3/7 0 calculator will give you value of 2t in first quadrant

6. cwrw238

right - set to rad arccos means the angle whose cos is given value or - on calculator button this might be cos -1

7. berrypicking

cos 3/7= .91 now what

8. berrypicking

how do I get the other value

9. cwrw238

you need cos-1 not cos check again : i make it 1.128 rad

10. berrypicking

ok that is 1.099??

11. berrypicking

1/cos(3/7) right?

12. berrypicking

and how do you know I need cos-1 and not cos?

13. cwrw238

no - the cosine of the angle 2t = 3/7 you need to find the angle whose cosine is 3/7 first find 3 / 7 on ur calculator then you need to press the cos-1 (or arccos) button

14. berrypicking

do I just press cos then -1

15. cwrw238

cos-1 does not mean 1 / cos in this context

16. cwrw238

no there is probably a button marked cos but you first press the shift key then cos button to get value of the angle

17. cwrw238

cos-1 notation is a bit confusing - in Europe they use arccos which makes more sense

18. berrypicking

cos (3/7)=.91. Do I press shift key before entering cos (3/7)? don't know the shift key

19. berrypicking

I haven't done any problems with cos-1

20. cwrw238

calculators vary you either press shift cos (3/7) or (3/7) shift cos

21. cwrw238

the correct value is 1.127 (to 3 dec places)

22. cwrw238

sorry 1.128

23. cwrw238

its a bit hard to explain without seeing your calculator....