- #1
H2instinct
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Homework Statement
Homework Equations
The hint.
The Attempt at a Solution
So using the hint I took the derivative of each of the parametrized functions.
[tex]\frac{dx}{d\theta} = -3sin(\theta)*cos^{2}(\theta)*a[/tex]
[tex]\frac{dy}{d\theta} = 3cos(\theta)*sin^{2}(\theta)*a[/tex]
Then I plugged them into this:
[tex]ds = \sqrt{dx^{2}+dy^{2}}d\theta[/tex]
Giving:
[tex]ds = 3*\left|a*sin(\theta)*cos(\theta)\right|d\theta[/tex]
[tex]\intds = \int3*\left|a*sin(\theta)*cos(\theta)\right|d\theta[/tex]
I know ds is infinitesimally small point on the original graph to measure slope, but I am still confused slightly about integrating both sides. Also assuming the absolute value goes away because sin and sos can only go from -1 to 1, so I took out the abs. value because I am assuming for positive number. Don't know if that's actually possible to do though.
[tex]s = \frac{-3*(cos(\theta))^{2}*a}{2}[/tex]This is where I need some pointing in the right direction.
Have been trying while waiting for some help:
Plugging into the other part of the hint:
[tex]ds = \sqrt{1 + \frac{-3sin(\theta)*cos^{2}(\theta)*a}{3cos(\theta)*sin^{2}(\theta)*a}}\left|-3sin(\theta)*cos^{2}(\theta)*a\right|[/tex]
Gives:
[tex]ds = 3*\left|a\right|(cos(\theta))^{2}*d\theta[/tex]
Tried integrating:
[tex]\intds = \int3*\left|a\right|(cos(\theta))^{2}d\theta[/tex]
Gives:
[tex]S = \frac{3*(sin(\theta)*cos(\theta)+\theta)*\left|a\right|}{2}[/tex]
Still not totally sure where to go with this.
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