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mathslover

Basic trigonometry help needed.

  • one year ago
  • one year ago

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  1. mathslover
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    Prove : \(\sin (90 - \theta) = \cos \theta\)

    • one year ago
  2. mathslover
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    Actually I am confused that how can I : prove that sin in 2nd quadrant is +ve ? That is my basic confusion ...

    • one year ago
  3. hartnn
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    can u use sin (A-B) formula?

    • one year ago
  4. mathslover
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    No idea. Actually that was just in start and the formula arises later, so I think that there must be an easier method?

    • one year ago
  5. hartnn
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    draw a right triangle

    • one year ago
  6. mathslover
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    :( not so good but OK ? :)

    • one year ago
  7. mathslover
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    |dw:1350046739720:dw| nothing is there without naming , OK now I think.

    • one year ago
  8. hartnn
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    |dw:1350046691525:dw| now find sin 90-theta and cos theta using basic defination

    • one year ago
  9. mathslover
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    OK wait please !

    • one year ago
  10. mathslover
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    In case of sin 90 - theta , will perpendicular be : adjacent (base) and base will be opposite?

    • one year ago
  11. hartnn
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    know the basic defination of sin and cos ? |dw:1350046897401:dw| apply it here, in terms of a and b,c

    • one year ago
  12. mathslover
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    OH IT IS soh cah toa and not soa cah toa , sorry :(

    • one year ago
  13. mathslover
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    sin = opposite / hypotenuse cos = adjacent / hypotenuse

    • one year ago
  14. hartnn
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    yup

    • one year ago
  15. mathslover
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    sin (90-theta) = b/c cos (theta) = b/c and hence sin(90-theta) = cos(theta) , got it now? lol jk. Well is this right @hartnn

    • one year ago
  16. hartnn
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    yep, hence proved.

    • one year ago
  17. hartnn
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    next identity please.

    • one year ago
  18. mathslover
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    prove that sin in 2nd quadrant is +ve ? That is my basic confusion ...

    • one year ago
  19. hartnn
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    here, put theta = -theta

    • one year ago
  20. hartnn
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    and use cos(-theta) = cos theta

    • one year ago
  21. mathslover
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    how to prove that cos(-theta)=theta ?

    • one year ago
  22. mathslover
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    again with the use of right triangle @hartnn ?

    • one year ago
  23. hartnn
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    how will u find -theta in triangle ?

    • one year ago
  24. mathslover
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    oh yes .. silly me . So, a cartesian plane ?

    • one year ago
  25. mathslover
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    no, cartesian plane will not work also.

    • one year ago
  26. sara12345
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    ccw : +ve angle cw : -ve angle

    • one year ago
  27. hartnn
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    because lengths will be positive , so ratio will always come out to be positive, hence, maybe cartesian plane won't work

    • one year ago
  28. mathslover
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    Some how agreed .

    • one year ago
  29. mathslover
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    searched net now, http://www.mathsisfun.com/algebra/trig-four-quadrants.html is that the correct one ?

    • one year ago
  30. hartnn
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    yes, its correct....we could prove it using co-ordinates.... (cos t,sin t)= (x,y) so sin t is +ve in 2nd quadrant

    • one year ago
  31. mathslover
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    doubts ended :) thanks a lo.

    • one year ago
  32. mathslover
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    *ton/lot.

    • one year ago
  33. hartnn
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    mathisfun is always a nice reference....

    • one year ago
  34. sara12345
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    more we knw more confuse we become

    • one year ago
  35. hartnn
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    more we practice, more the confusion vanishes....

    • one year ago
  36. sara12345
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    more we practice, more ways we look at things n hence more confusions which ofcourse gives kick ;p

    • one year ago
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