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Math Help - Absolute values in differential equations.

  1. #1
    Senior Member Stroodle's Avatar
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    Absolute values in differential equations.

    Hi,

    I've been taught that when integration involves logs like y=\int\frac{1}{x}\ dx, you must express your answer as the log of an absolute value unless that value is known to be positive. e.g. in this case y=log_e\left | x \right |+c.
    But in my textbook, it rarely uses absolute values, and just states the answers in the form y=log_e(x)+c, which then obviously changes the solutions to many differential equations.

    Am I right to use the absolute value, or am I missing something?

    Thanks for your help
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by Stroodle View Post
    Hi,

    I've been taught that when integration involves logs like y=\int\frac{1}{x}\ dx, you must express your answer as the log of an absolute value unless that value is known to be positive. e.g. in this case y=log_e\left | x \right |+c.
    But in my textbook, it rarely uses absolute values, and just states the answers in the form y=log_e(x)+c, which then obviously changes the solutions to many differential equations.

    Am I right to use the absolute value, or am I missing something? Mr F says: You are right.

    Thanks for your help
    ..
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