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Edexcel C4 - Exercise 4B - Question 1G (page 40 of the new textbook) Watch

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    This question has confused me for the past hour or so, I simply can't get to the answer. Any help would be appreciated

    Find and expression in terms of x and y for dy/dx, given that:

    (x-y)^4=x+y+5

    thanks!!!
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    Have you differentiated it implicitly?

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    yes and i ended up with: 4(x-y)^3(1-dy/dx)=1+dy/dx have no clue what to do next!!! btw i got the left hand side by using chain rule.
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    (Original post by harris12345)
    yes and i ended up with: 4(x-y)^3(1-dy/dx)=1+dy/dx have no clue what to do next!!! btw i got the left hand side by using chain rule.
    Rearrange this to find dy/dx.
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    (Original post by brittanna)
    Rearrange this to find dy/dx.
    thats the part where im struggling. the question seems different to others in the same exercise.
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    (Original post by harris12345)
    thats the part where im struggling. the question seems different to others in the same exercise.
    So you have 4(x-y)^3(1-\frac{dy}{dx})=1+dy/dx

    Then 4(x-y)^3 - 4(x-y)^3\frac{dy}{dx} = 1 + \frac{dy}{dx}.

    4(x-y)^3 - 1 = \frac{dy}{dx}\left(1+4(x-y)^3\right).

    Can you see what to do from here? Does this all make sense?
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    (Original post by brittanna)
    So you have 4(x-y)^3(1-\frac{dy}{dx})=1+dy/dx

    Then 4(x-y)^3 - 4(x-y)^3\frac{dy}{dx} = 1 + \frac{dy}{dx}.

    4(x-y)^3 - 1 = \frac{dy}{dx}\left(1+4(x-y)^3\right).

    Can you see what to do from here? Does this all make sense?
    how did u get the -4(x-y)^3dy/dx in the second step?
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    (Original post by harris12345)
    how did u get the -4(x-y)^3dy/dx in the second step?
    I multiplied out the bracket. a(b-c) = ab - ac.

    Just let a = 4(x-y)^3, b=1, c=\frac{dy}{dx}.
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    (Original post by brittanna)
    I multiplied out the bracket. a(b-c) = ab - ac.

    Just let a = 4(x-y)^3, b=1, c=\frac{dy}{dx}.
    aaah that all makes sense. I appreciate the help mate thanks for takin out ur time!!
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    thank you, really helpful
 
 
 
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