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The last big toughy

  1. Jan 4, 2004 #1
    Ok the last question on those pages of question is this and i have got stuck and cant figure it out. I need to show that (ds=degrees)
    Sin(45ds+x) +cos(45ds+x) = sqaureroot2 cosx.
    Ok so i did left side first and changed it to.
    Sin45Cosy + Cos45Siny +Cos45Cosy - Sin45Siny
    Now what i want to do is divide out the CosY and Sin Y but even if i do that it doesnt make square root two and i dont know what to do from there. Can you help me solve this last practise question.
  2. jcsd
  3. Jan 4, 2004 #2
    They've given you a trig problem that includes the sine and cosine of
    a special angle. That should prod you in the right direction. If not, look at the attached text file.

    Attached Files:

  4. Jan 4, 2004 #3


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    Staff Emeritus
    Science Advisor

    What you are doing doesn't make a whole lot of sense. What is Y?

    sin(45+ x)= sin(45)cos(x)+ cos(45)sin(x) and
    cos(45+ x)= cos(45)cos(x)- sin(45)sin(x).

    Do you know what sin(45) and cos(45) are?

    Plug those into the two equations above and add.
  5. Jan 4, 2004 #4
    Oh ok i get it, ya i thought of putting the 1/root2 in but wasnt sure how to go from there but i understand now. Thankyou so much!
  6. Jan 4, 2004 #5

    how old are you buddy?
  7. Jan 4, 2004 #6
    16 currently in grade 11. Why?
  8. Jan 4, 2004 #7
    Re: Re: The last big toughy

    Haven't you discovered the "Profile" button yet, buddy? :)
  9. Jan 4, 2004 #8
    Just testing out the "math typesetting" thing:

    \sin(45^\circ + x) &= \sin(45^\circ) \cos x + \cos(45^\circ) \sin x \\
    &= \frac{\cos x}{\sqrt{2}} + \frac{\sin x}{\sqrt{2}} \\
    &= \frac{\cos x + \sin x}{\sqrt{2}}
  10. Jan 4, 2004 #9

    lol which state are you in?
  11. Jan 4, 2004 #10
    Im in Ontario Canada. Its a province not a state.
  12. Jan 8, 2004 #11
    are you in the canadian school system?
  13. Jan 8, 2004 #12
    Yes i am, i am glad you are all so interested in me. I feel so special :wink:
  14. Jan 9, 2004 #13
    heh, it sounded alot like one of our A-level questions, i was curious about it. :wink:
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