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gruba
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Homework Statement
Find area bounded by parabola [itex]y^2=2px,p\in\mathbb R[/itex] and normal to parabola that closes an angle [itex]\alpha=\frac{3\pi}{4}[/itex] with the positive [itex]Ox[/itex] axis.
Homework Equations
-Area
-Integration
-Analytic geometry
The Attempt at a Solution
For [itex]p>0[/itex] we can find the normal to parabola such that it closes an angle [itex]\alpha[/itex] with positive [itex]Ox[/itex] axis. For [itex]p<0[/itex] we can't find a normal on parabola for given condition.
Point [itex]A[/itex] in first quadrant where the angle between positive [itex]Ox[/itex] axis and parabola is found by
[itex]y=\sqrt{2px},y'=1\Rightarrow A\left(\frac{p}{2},p\right),p>0[/itex].
Now we can find the line that contains point [itex]A[/itex]:
[itex]y-p=-x+\frac{p}{2}\Rightarrow y=-x+\frac{3p}{2},p>0[/itex].
This is the normal on parabola that satisfies the condition for [itex]\alpha[/itex].
Second point of the normal is found by solving the system:
[itex]y=-x+\frac{3p}{2},y^2=2px\Rightarrow x=\frac{3p}{2}-y\Rightarrow y_1=-3p,y_2=p[/itex]. Point [itex]B[/itex] has to be in the fourth quadrant, so [itex]B=\left(\frac{9p}{2},-3p\right),p>0[/itex].
Now the problem is reduced: Find the area bounded by [itex]y^2=2px[/itex] and [itex]y=-x+\frac{3p}{2}[/itex] where [itex]p>0[/itex] which is the area [itex]AOB[/itex].
How to integrate these functions to get the area?
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