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Either my math book is wrong or my calculator doesn't work

  1. Aug 19, 2011 #1
    This book says that sin of 45 degrees is .70

    My calculator which is a TI 83 says it's .85, plus this website also says it's .85



    Who is right?
  2. jcsd
  3. Aug 19, 2011 #2
    Ok, this website
    gives me the answer .70, but I would still like to know why a TI 83 is wrong
  4. Aug 19, 2011 #3
    The books right. Your calculator is calculating it in Radians. Switch it to degree's and it\l give you the right answer.
  5. Aug 19, 2011 #4
    It's a units problem. [itex]45^{\circ} = {\pi \over 4}[/itex]. Indeed [itex]\sin 45^{\circ} \approx 0.707[/itex], when the argument of sin is measured in degrees, but [itex]\sin 45 \approx 0.85[/itex] since the 45 here is measured in radians. You have to tell your calculator to use a different unit of angle measurement.
  6. Aug 19, 2011 #5
    Always remember, when you turn your calculator on, press "Mode" to make sure it's in the correct angle unit measurement. You should be in degrees, but if you're in precal or trig, you'll move to radians pretty quick. If you're in geometry, you'll stay with degrees, so you'll have to switch it back to degrees every time you reset it. When reset, it defaults to radians.
  7. Aug 19, 2011 #6


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    Also, be careful with your significant digits bobsmith, otherwise both answers are wrong. If you are going to write 2 significant digits then it has to be 0.71 :)
  8. Aug 19, 2011 #7
    LOL! But, I think he's in geometry, which is typically a sophomore class. Most high school kids don't learn sig. figs. until chemistry, because it's not expected of them until they get to a high level science class (like chemistry).
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