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ketz

  • one year ago

Can anybody explain tom me why when solving cos x >0.69? ...The answer is x<46.4 degrees?? why the inequality sign changes?

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  1. kc_kennylau
    • one year ago
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    Do you have the graph of cosine?

  2. kc_kennylau
    • one year ago
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    Actually, the value of cosine goes down when x goes up

  3. ketz
    • one year ago
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    So inequality signs are not only supposed to be flipped when divide by negative number or multiply by negative number??

  4. ketz
    • one year ago
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    I thought it was only for the condition i stated above that inequality changes sign!!

  5. kc_kennylau
    • one year ago
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    Well, there are many conditions in which the inequality changes sign

  6. kc_kennylau
    • one year ago
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    You aren't multiplying something to the inequality here

  7. ketz
    • one year ago
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    Can you enumerate all of them please...

  8. kc_kennylau
    • one year ago
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    Well, in general, when you apply decreasing functions to both sides of an inequality, it changes signs.

  9. kc_kennylau
    • one year ago
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    Decreasing functions are those whose graphs go down.

  10. kc_kennylau
    • one year ago
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    |dw:1434221346342:dw|

  11. kc_kennylau
    • one year ago
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    This is a part of the cosine graph

  12. kc_kennylau
    • one year ago
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    You can see that if \(\cos x > 0.69\), \(x < \ \)something.

  13. ketz
    • one year ago
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    Thxs...Is there any other conditions to change the inequality sign? Can you provide a link...

  14. kc_kennylau
    • one year ago
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    Okay, those functions are called "decreasing functions". I'm searching for a list.

  15. kc_kennylau
    • one year ago
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    I can't really find a list available...

  16. ketz
    • one year ago
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    but how do you know all of them?

  17. kc_kennylau
    • one year ago
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    I can't know all of them, but in the case of cosine, I know the shape of the cosine graph.

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