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C3 Differentiation question :/

I don't understand why I can't get this right.

Given that y = 1/(4x+1)^2 find the value of dy/dx at (1/4,1/4)

Do I open the brackets or do I differentiate the two functions?

The answers -1 btw
y=1/(4x+1)^2=(4x+1)^-2 which you can differentiate using the chain rule u=4x+1
then one you have dy/dx just sub in x and there's your answer
Original post by Jonario
I don't understand why I can't get this right.

Given that y = 1/(4x+1)^2 find the value of dy/dx at (1/4,1/4)

Do I open the brackets or do I differentiate the two functions?

The answers -1 btw


Chain rule?
Note that y=(4x+1)−2y=(4x+1)^{-2}. If you can't do it by recognition, let u=4x+1u=4x+1 so y=u−2y=u^{-2}. Then find dudx\frac{du}{dx} and dydu\frac{dy}{du} and note that dydx=dydu×dudx\frac{dy}{dx}=\frac{dy}{du} \times \frac{du}{dx}.
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Jonario
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Original post by Farhan.Hanif93
Chain rule?
Note that y=(4x+1)−2y=(4x+1)^{-2}. If you can't do it by recognition, let u=4x+1u=4x+1 so y=u−2y=u^{-2}. Then find dudx\frac{du}{dx} and dydu\frac{dy}{du} and note that dydx=dydu×dudx\frac{dy}{dx}=\frac{dy}{du} \times \frac{du}{dx}.


Thanks, my teacher taught me different way of finding dy/dx, the only problem i had was identifying that 1/(4x+2)^2 was (4x+2)^-2

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