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    Once again my simple maths is failing me! I have an example for a 1st order ODE, and it is showing me how to use the integrating factor method. I says I first need to re-express the equation from

    x(dy/dx)+y=x to d/dx(xy)=x

    I am failing to see how this has happened an really need to if I am able to do my homework! Any helps?
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    If you know how to do integrating factors, simplify the equation, find the IF, and multiply by it.
    If not, just notice that xy'+y=(xy)' where ' means 'differentiated wrt x'.
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    product rule

    d/dx(xy) = d/dx(x)·y + x·d/dx(y) = y + x(dy/dx)
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    (Original post by dichr0ic)
    product rule

    d/dx(xy) = d/dx(x)·y + x·d/dx(y) = y + x(dy/dx)
    Ah that might be it!
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    (Original post by doggyfizzel)
    Ah that might be it!
    is it one of the examples in old spec FP1 textbook? i remember being confused about this too, then i realised it was the product rule :proud:
 
 
 
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Updated: January 27, 2010
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