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-   -   proving trig identities ((secx-tanx)^2 1)/(secxcscx-tanxcscx)=2tanx (https://www.askmehelpdesk.com/showthread.php?t=619220)

  • Dec 12, 2011, 09:59 PM
    hines57
    proving trig identities ((secx-tanx)^2 1)/(secxcscx-tanxcscx)=2tanx
    ((secx-tanx)^2 1)/(secxcscx-tanxcscx)=2tanx
  • Dec 12, 2011, 10:17 PM
    LuckyChucky13
    Is the first bracket to the power of 21?
  • Dec 12, 2011, 10:21 PM
    hines57
    sorry its 2+1 ((secx-tanx)^2+1)/(secxcscx-tanxcscx)=2tanx
  • Dec 12, 2011, 10:51 PM
    LuckyChucky13
    I will try to show it below, if it's not too clear (since it's not mathematically friendly, let me know and I will keep trying:

    Here goes:

    This is for the numerator (the top part)
    First, expand the bracket (that is, multiply it by itself)

    So you get: Sec^2 (x) - 2 Sec(x)tan(x) + tan^2(x) + 1
    Now, one of the identities is that tan^2(x) + 1 is equal to sec^2(x), s the numerator becomes:

    2sec^2(x) - 2sec(x)tan(x)
    Now factor out the 2sec(x), which is common to both terms and you get:
    2sec(x) {sec(x) - tan(x)}

    For the denominator, factor out the csc(x) so you get:
    csc(x) {sec(x) - tan(x)}

    Cancel the common brackets from the numerator and denominator (which is {sec(x)tan(x)} and you're left with:

    2sec(x) / csc(x)

    this simplifies to 2 (1/cos(x) / 1/sin(x))
    now, when dividing by a fraction, we multiply by its reciprocal, so we get:

    2 (1/cos(x) * sin(x)/1)

    which simplifies to 2tan(x).

    If anything is not clear, let me know...

    Good luck.
  • Dec 12, 2011, 10:52 PM
    LuckyChucky13
    I will try to show it below, if it's not too clear (since it's not mathematically friendly, let me know and I will keep trying:

    Here goes:

    This is for the numerator (the top part)
    First, expand the bracket (that is, multiply it by itself)

    So you get: Sec^2 (x) - 2 Sec(x)tan(x) + tan^2(x) + 1
    Now, one of the identities is that tan^2(x) + 1 is equal to sec^2(x), s the numerator becomes:

    2sec^2(x) - 2sec(x)tan(x)
    Now factor out the 2sec(x), which is common to both terms and you get:
    2sec(x) {sec(x) - tan(x)}

    For the denominator, factor out the csc(x) so you get:
    csc(x) {sec(x) - tan(x)}

    Cancel the common brackets from the numerator and denominator (which is {sec(x)tan(x)} and you're left with:

    2sec(x) / csc(x)

    this simplifies to 2 (1/cos(x) / 1/sin(x))
    now, when dividing by a fraction, we multiply by its reciprocal, so we get:

    2 (1/cos(x) * sin(x)/1)

    which simplifies to 2 (sin(x) / cos(x)) and in turn you ger: 2tan(x).

    If anything is not clear, let me know...

    Good luck.

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