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## Homework Statement

A particle is moving along the curve [itex]y=\sqrt{x}[/itex]. As the particle passes through the point (4,2), its x-coordinate increases at a rate of 3 cm/s. How fast is the distance from the particle to the origin changing at this instant?

## Homework Equations

## The Attempt at a Solution

I made a diagram of the curve, connected the point (4,2), x=4, and the origin by a right triangle with z being the hypotenuse, x = 4, and y = 2.

so [itex]z^2=x^2+y^2[/itex], after differentiating I arrive at

[tex]\frac{dz}{dt}=\frac{1}{z}(x\frac{dx}{dt}+\frac{dy}{dt})[/tex]

i know dx/dt 3 cm/s, but I have no idea how to find dy/dt, I have a feeling that I have to use the equation of the curve but I'm not sure at all

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