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MTALHAHASSAN2

  • one year ago

Need help!! 2. Give that cos (x+y) = cos x cos y – sin x sin y, use this to express cos 2x in terms of cos x

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  1. campbell_st
    • one year ago
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    so replace y with x so you have cos(x + x) = cos(x)cos(x) - sin(x)sin(x) and simplify from there.

  2. campbell_st
    • one year ago
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    so the left side of the equation becomes cos(2x)

  3. MTALHAHASSAN2
    • one year ago
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    why do you do that

  4. campbell_st
    • one year ago
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    now you can simplify the right side

  5. MTALHAHASSAN2
    • one year ago
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    I mean why do you change the y into x

  6. campbell_st
    • one year ago
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    that way when you replace y with x cos(x + y) = cos(x + x) which is cos(2x)

  7. MTALHAHASSAN2
    • one year ago
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    |dw:1437707497195:dw|

  8. MTALHAHASSAN2
    • one year ago
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    right

  9. campbell_st
    • one year ago
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    thats correct.... but the question asks in terms of cos(x) so what do you know about sin^2(x)..?

  10. MTALHAHASSAN2
    • one year ago
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    sin2x = 2sinx cosx

  11. campbell_st
    • one year ago
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    no its \[\sin^2(x) \]

  12. MTALHAHASSAN2
    • one year ago
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    is there is any formula for this

  13. MTALHAHASSAN2
    • one year ago
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    I don't have it for this one I have for Sin2x

  14. campbell_st
    • one year ago
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    sure its one of the fundamentals \[\cos^2(x) + \sin^2(x) = 1\]

  15. MTALHAHASSAN2
    • one year ago
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    oh know it be sin^2 (x) = 1-cos^2x

  16. MTALHAHASSAN2
    • one year ago
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    = cos^2 x -(1-cos^2 x)

  17. MTALHAHASSAN2
    • one year ago
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    @campbell_st

  18. MTALHAHASSAN2
    • one year ago
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    @mathway

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