SOLUTION: An airplane is flying along the hyperbolic path illustrated in the figure. If an equation of the path is 2y^2-x^2=8 , determine how close the airplane comes to a town located at

Algebra ->  Quadratic-relations-and-conic-sections -> SOLUTION: An airplane is flying along the hyperbolic path illustrated in the figure. If an equation of the path is 2y^2-x^2=8 , determine how close the airplane comes to a town located at      Log On


   



Question 1082518: An airplane is flying along the hyperbolic
path illustrated in the figure. If an equation of the path
is 2y^2-x^2=8 , determine how close the airplane comes to
a town located at (3,0). (Hint: Let S denote the square of
the distance from a point on the path to(3,0), and
find the minimum value of S.)

Answer by ikleyn(52794) About Me  (Show Source):
You can put this solution on YOUR website!
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An airplane is flying along the hyperbolic path illustrated in the figure.
If an equation of the path is 2y^2-x^2=8 , determine how close the airplane comes to a town located at (3,0).
(Hint: Let S denote the square of the distance from a point on the path to(3,0), and find the minimum value of S.)
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1.  Our curve is specific !  If (x,y) is the point on the curve then

    2y^2 - x^2 = 8,  which implies  y^2 = %288%2Bx%5E2%29%2F2.   (1)



2.  The distance from ANY point (x,y) on the coordinate plane to the point (3,0) is

    d%5E2 = %28x-3%29%5E2+%2B+y%5E2.    (2)

    Now, if the point lies on the hyperbola, you have (1), and you can substitute this expression for y%5E2 into the formula (2).

    You will get

    d%5E2 = %28x-3%29%5E2 + %288%2Bx%5E2%29%2F2 = x%5E2+-+6x+%2B+9+%2B+4 + x%5E2%2F2 = %283%2F2%29%2Ax%5E2+-+6x+%2B+13.   (3)

    So, you need to minimize (3). In other words, you need to find the value of "x" which minimizes this quadratic function.



4.  The quadratic function of the general form q(x) = ax%5E2+%2B+bx+%2B+c achieves the maximum at x = -b%2F%282a%29.

    In your case this "x" is x = - %28%28-6%29%29%2F%282%2A%283%2F2%29%29 = 6%2F3 = 2.


    So, we found the value of "x". It is x= 2.

    Then the corresponding value of "y" on your curve is 

         2y%5E2+-+2%5E2 = 8  ---->  2y%5E2 = 8 + 4 = 12  ---->  y%5E2 = 12%2F2 = 6.

     Thus your "closest" point on the curve is  (x,y) = (2,sqrt%286%29).



5.  Now you can find that minimal distance:

    d%5E2 = %28x-3%29%5E2+%2B+y%5E2 = %282-3%29%5E2+%2B+6 = 1 + 6 = 7.


    Hence, the minimal distance itself is  sqrt%287%29 = 2.646 (approximately).

My congratulations !   The problem is solved.