Find the derivative dy/dx if x^2+y^2=7, in terms of x and y. We differentiate both sides of the equation using the chain rule, and the fact that (dx)/(dx)=1. We then obtain: 2x(dx)/(dx)+2y(dy)/(dx)=0, that is 2x+2y(dy)/(dx)=0 So my question is totally basic: what does (dx)/(dx) stand for? What's it doing in there in the first place?

Ledexadvanips

Ledexadvanips

Answered question

2022-08-12

Find the derivative d y / d x if x 2 + y 2 = 7, in terms of x and y. We differentiate both sides of the equation using the chain rule, and the fact that d x / d x = 1. We then obtain:
2 x d x d x + 2 y d y d x = 0, that is 2 x + 2 y d y d x = 0
So my question is totally basic: what does d x d x stand for? What's it doing in there in the first place? I thought x 2 could be differentiated directly to 2 x, without any intermediate steps, and I'm just not seeing what d x d x is doing in there. Thanks for any tips.

Answer & Explanation

Gillian Howell

Gillian Howell

Beginner2022-08-13Added 17 answers

The d x d x is due to the chain rule. It means what other differentials mean: the rate of change of x with respect to the rate of change of... well, x in this case!
Since x changes at the same rate as itself
this ratio is equal to 1
And yes, the derivative of x 2 , with respect to x, is 2 x.

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