How Do Parametric Curves and u-Substitution Relate to Length Calculation?

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SUMMARY

The discussion focuses on calculating the length of a parametric curve defined by the equations x = t^3 and y = (3t^2)/2 for the interval 0 ≤ t ≤ √3. The correct approach involves using the formula for arc length, which requires the square root of the sum of the squares of the derivatives, specifically √((dx/dt)² + (dy/dt)²). The participant incorrectly attempted to simplify the expression by adding the derivatives directly, which violates the mathematical principle that √(a² + b²) ≠ a + b. The necessity of u-substitution in this context is questioned, highlighting a misunderstanding of its application in length calculations.

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Homework Statement



x = t^3, y = (3t^2)/2 0<= t <= √3


The Attempt at a Solution



dx/dt = 3t^2
dy/dt = 3t

step 1. √((3t^2)^2 + (3t)^2)

step 2. 3t^2 + 3t

(the book says I can't do that, I don't see why)

step 3. insert √3 into t

Here's the books solution

Screenshot2012-02-04at82009PM.png


I understand u substitution but I don't see why it's necessary here. I don't why my method does not follow all the rules.
 
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Because ##\sqrt{a^2+b^2} \ne a+b##. Try it with a=b=1, for instance.
 

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