Finding the Length of y = x^{3/2} from x = 0 to x = 4

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The discussion focuses on calculating the length of the curve defined by the equation y = x^{3/2} from x = 0 to x = 4 using the formula L = ∫ from a to b √(1 + (dy/dx)²) dx. The correct derivative dy/dx is 3/2 * x^{1/2}, leading to the integral L = ∫ from 0 to 4 √(1 + (9/4)x) dx. The initial calculation resulting in 64/27 was incorrect, and participants emphasized the importance of changing limits of integration when applying the substitution rule.

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Homework Statement


Find the length of the curve. y = x^{3/2} from x = 0 to x = 4.


Homework Equations


L = \int^{b}_{a} \sqrt{1 + (dy/dx)^{2}} dx


The Attempt at a Solution


L = \int^{b}_{a} \sqrt{1 + (dy/dx)^{2}} dx
L = \int^{4}_{0} \sqrt{1 + (3x^{1/2}/2)^{2}} dx
.
.
.
.
I used substitution rule
.
.
.
L = 64/27

Is this correct?

Thanks
 
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Precursor said:

Homework Statement


Find the length of the curve. y = x^{3/2} from x = 0 to x = 4.


Homework Equations


L = \int^{b}_{a} \sqrt{1 + (dy/dx)^{2}} dx


The Attempt at a Solution


L = \int^{b}_{a} \sqrt{1 + (dy/dx)^{2}} dx
L = \int^{4}_{0} \sqrt{1 + (3x^{1/2}/2)^{2}} dx
.
.
.
.
I used substitution rule
.
.
.
L = 64/27

Is this correct?

Thanks


http://www.wolframalpha.com/input/?i=integrate+sqrt[+1+++[+(3/2)+x^(1/2)+]^2+]+from+x=0+to+x=4
Its better to post all of your work.
 
Precursor said:
So my answer is wrong afterall?

By the way, thanks a lot for that website! If only I knew such a website existed before. :smile:

Yeah Its wrong.

You will face: \int_0^4 \sqrt{ 1 + \frac{9}{4}x } \;\ dx
What did you do for it?
 
Actually I found c(7 \sqrt{7} - 1),
where c is a numerical factor (I got 2/3) which I'm not sure of because I did the calculation sloppily.
So I suggest you show the rest of the calculation as well.

[edit] Too slow, you already have several replies. [/edit]
 
Ratio Test =) said:
Yeah Its wrong.

You will face: \int_0^4 \sqrt{ 1 + \frac{9}{4}x } \;\ dx
What did you do for it?

That's exactly what I got, but when I used the substitution rule, to integrate, I did not change the limits of integration to in terms of u.
 
Precursor said:
That's exactly what I got, but when I used the substitution rule, to integrate, I did not change the limits of integration to in terms of u.

Ohhh.
BTW, Its a famous mistake. :)
 

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