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Math Help - Finding the differential of dy

  1. #1
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    Question Finding the differential of dy

    Let

    Find the differential when and

    Find the differential when and

    so far i came up with dy/dx = 10x+7

    dy = [10x+7]dx

    so now i am confused and i don't know if i did that right and i need to know what to do next
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  2. #2
    Member Jskid's Avatar
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    I believe you should have put this in the differential equation section of the forum, not calculus.
    PM a moderator and get them to move your post.
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  3. #3
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    Quote Originally Posted by jpratt View Post

    so far i came up with dy/dx = 10x+7

    dy = [10x+7]dx

    so now i am confused and i don't know if i did that right and i need to know what to do next
    Substitute some values in?
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  4. #4
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    Quote Originally Posted by Jskid View Post
    I believe you should have put this in the differential equation section of the forum, not calculus.
    PM a moderator and get them to move your post.
    No, just "finding differentials" has nothing to do with differential equations.
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  5. #5
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    Quote Originally Posted by jpratt View Post
    Let

    Find the differential when and

    Find the differential when and

    so far i came up with dy/dx = 10x+7

    dy = [10x+7]dx

    so now i am confused and i don't know if i did that right and i need to know what to do next
    Yes, that is the general formula for dy. Now just do what they say: set x= 1, dx= .03 and do the arithmetic.
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  6. #6
    MHF Contributor chisigma's Avatar
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    In my opinion the terms dx and dy don't indicate differentials but finite differences [otherwise an expression like dx= .3 is meaningless...]. In that case writing in the equation...

    y = 5\ x^{2} + 7\ x + 4 (1)

    ... y + dy instead of y and x + dx instead of x You obtain...

    y + dy = 5\ (x + dx)^{2} + 7\ (x+dx) + 4 \rightarrow dy = 10\ x\ dx + 5\ dx^{2} + 7\ dx (2)

    ... that allows You to find the solution...

    Kind regards

    \chi \sigma
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