document.write( "Question 1039422: P (2p,p^2) is a variable point on the parabola x^2 = 4y. N is the foot of the perpendicular form P to the x axis NR is perpendicular to OP.\r
\n" ); document.write( "\n" ); document.write( "a. find the equation of OP
\n" ); document.write( "b. find the equation of NR
\n" ); document.write( "c. show that the R has coordinates (8p/p^2 +4 , 4p^2/p^2+4)
\n" ); document.write( "d. show that the locus R is a circle and state its centre and radius\r
\n" ); document.write( "\n" ); document.write( "NEED HELP WITH PART C AND D!!!
\n" ); document.write( "

Algebra.Com's Answer #654251 by KMST(5328)\"\" \"About 
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a. {{OP}}} connect \"O%280%2C0%29\" and \"P%282p%2Cp%5E2%29\" ,
\n" ); document.write( "so its slope is \"p%5E2%2F2p=p%2F2\" and its y-intercept is \"0\" .
\n" ); document.write( "The equation of \"OP\" is \"y=%28p%2F2%29x\"
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\n" ); document.write( "b. The foot of the perpendicular form \"P%282p%2Cp%5E2%29\" to the x-axis is
\n" ); document.write( "\"N%282p%2C0%29\" , and the slope of a line perpendicular to \"OP\" is
\n" ); document.write( "\"-1%2F%28p%2F2%29=-2%2Fp\" .
\n" ); document.write( "So, the equation of \"NR\" in point-slope form, based on point \"N%282p%2C0%29\" is
\n" ); document.write( "\"y=%28-2%2Fp%29%28x-2p%29\"
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\n" ); document.write( "c. you did not tell me where point \"R\" is, but from its coordinates, I see that is a point on line \"OP\" .
\n" ); document.write( "so, R must be the intersecion of NR and OP.
\n" ); document.write( "Hence, its coordinates are the solution to
\n" ); document.write( "\"system%28y=%28p%2F2%29x%2Cy=%28-2%2Fp%29%28x-2p%29%29\" .
\n" ); document.write( "Using substitution, we start trying to find \"x\" from \"%28-2%2Fp%29%28x-2p%29=%28p%2F2%29x\" .
\n" ); document.write( "Multiplying both sides times \"-2p\" we get
\n" ); document.write( "\"%28-2p%29%28-2%2Fp%29%28x-2p%29=%28-2p%29%28p%2F2%29x\" .
\n" ); document.write( "\"4%28x-2p%29=-p%5E2x\"
\n" ); document.write( "\"4x-8p=-p%5E2x\"
\n" ); document.write( "\"4x%2Bp%5E2x=8p\"
\n" ); document.write( "\"%284%2Bp%5E2%29x=8p\"
\n" ); document.write( "\"highlight%28x=8p%2F%284%2Bp%5E2%29%29\" .
\n" ); document.write( "Then, substituting the value found for \"x\" into \"y=%28p%2F2%29x\" we get
\n" ); document.write( "\"y=%28p%2F2%29%288p%2F%284%2Bp%5E2%29%29\"
\n" ); document.write( "\"highlight%28y=4p%5E2%2F%284%2Bp%5E2%29%29\"
\n" ); document.write( "
\n" ); document.write( "d. \"R%288p%2F%284%2Bp%5E2%29%2C4p%5E2%2F%284%2Bp%5E2%29%29\" is symmetrical with respect to the y-axis,
\n" ); document.write( "because substituting \"-p\" for \"p\" you get point \"S%28-8p%2F%284%2Bp%5E2%29%2C4p%5E2%2F%284%2Bp%5E2%29%29\" ,
\n" ); document.write( "the reflection of \"R%288p%2F%284%2Bp%5E2%29%2C4p%5E2%2F%284%2Bp%5E2%29%29\" across the y-axis.
\n" ); document.write( "Making \"p=0\" gives us the point \"O%280%2C0%29\" , which is part of the locus or \"R\" .
\n" ); document.write( "All the points \"R%288p%2F%284%2Bp%5E2%29%2C4p%5E2%2F%284%2Bp%5E2%29%29\" have a non-negative y-coordinate,
\n" ); document.write( "\"y=4p%5E2%2F%284%2Bp%5E2%29%3E=0\" .
\n" ); document.write( "So the circle should be centered on the y-axis,
\n" ); document.write( "pass though \"O%280%2C0%29\" ,
\n" ); document.write( "and otherwise be above the y-axis.
\n" ); document.write( "Such a circle has a radius r, and is centered at \"C%280%2Cr%29\" .
\n" ); document.write( "All we need to do is find \"r\" .
\n" ); document.write( "The equation of such a circle would be
\n" ); document.write( "\"%28x-0%29%5E2%2B%28y-r%29%5E2=r%5E2\" <---> \"x%5E2%2By%5E2-2ry%2Br%5E2=r%5E2\" <---> \"x%5E2%2By%5E2-2ry=0\" <---> \"x%5E2%2By%5E2=2ry\" .
\n" ); document.write( "Substituting \"x=8p%2F%284%2Bp%5E2%29\" and \"y=4p%5E2%2F%284%2Bp%5E2%29\" , we can find \"r\" .
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\n" ); document.write( "\"64p%5E2%2F%284%2Bp%5E2%29%5E2%2B16p%5E4%2F%284%2Bp%5E2%29%5E2+=+8rp%5E2%2F%284%2Bp%5E2%29\"
\n" ); document.write( "\"64p%5E2%2B16p%5E4+=+8rp%5E2%284%2Bp%5E2%29\"
\n" ); document.write( "\"16p%5E2%284%2Bp%5E2%29+=+8rp%5E2%284%2Bp%5E2%29\"
\n" ); document.write( "\"16p%5E2=+8rp%5E2\"
\n" ); document.write( "\"16p%5E2%2F8p%5E2=r\" ---> \"highlight%28r=2%29\" .
\n" ); document.write( "The locus of \"R\" is a circle of radius \"2\" centered at \"C%280%2C2%29\" .
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\n" ); document.write( "NOTES:
\n" ); document.write( "The equations to graph that circle: \"system%28x=8p%2F%284%2Bp%5E2%29%2Cy=4p%5E2%2F%284%2Bp%5E2%29%29\"
\n" ); document.write( "can be called parametric equations.
\n" ); document.write( "Parametric equations allow us to show a relation that is not a function,
\n" ); document.write( "so we can express a relation that graphs as a curve we call a parametric curve.
\n" ); document.write( "They are very useful if would be difficult to express with just \"x\" and \"y\" .
\n" ); document.write( "A third variable called parameter (in this case \"p\" ) is uaed,
\n" ); document.write( "and we define \"x\" and \"y\" as functionc of that parameter.
\n" ); document.write( "Many times, we try to \"eliminate the parameter\",
\n" ); document.write( "to get to a relation between just \"x\" and \"y\" ,
\n" ); document.write( "be able to understand the relation between \"x\" and \"y\" more easily.
\n" ); document.write( "One way to do that is to solve one equation for the parameter,
\n" ); document.write( "getting an expression for the parameter in terms of \"x\" and \"y\" that can be substituted for the parameter in the other equation for the other variable.
\n" ); document.write( "That would have been complicated in this case, but fortunately we were told it was a circle and all we had to do is prove it and find center and radius.
\n" ); document.write( "That made it easier.
\n" ); document.write( "Maybe the way I went about it is not the expected way, but it was the easiest way I could figure out.
\n" ); document.write( "If you find out about some easier way, let me know.\r
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