Monday, March 30, 2015

Determine all the points of intrsection of the lines y=12/x and y^2=(3x^2+5)/2?

To determine the intercepting point of the curves (not
lines), we'll have to solve the system of equations of the
curves.


We'll write the
system:


2y^2 =3x^2+5


3x^2 -
2y^2 = -5 (1)


xy = 12 (2)


We
recognize an a homogenous system and the solving strategy is to eliminate the numbers
alone.


For this reason, we'll multiply the 1st equation by
12 and the 2nd equation by 5:


36x^2 - 24y^2 = -60
(3)


5xy = 60 (4)


We'll add (3)
and (4):


36x^2 + 5xy - 24y^2 =
0


We'll divide by x^2:


36 +
5y/x - 24y^2/x^2 = 0


We'll substitute y/x =
t:


-24t^2 + 5t + 36 = 0


24t^2
- 5t - 36 = 0


We'll apply quadratic
formula:


t1 =
[5+sqrt(25+3456)]/48


t1 =
(5+59)/48


t1 = 4/3


t2 =
(5-59)/48


t2 = -9/8


We'll put
y/x = 4/3


y = 4x/3


We'll
substitute y in the 2nd equation:


x*(4x/3) =
12


4x^2 = 4*9


x^2 =
9


x1 = 3 and x2 = -3


y1 = 4
and y2 = -4


y/x = -9/8


y =
-9x/8


-9x^2 = 8*12


-3x^2 =
32


x^2 = -32/3


This equation
has no real solutions.


The intercepting
points of the curves are represented by the following real solutions of the system, that
are: {(3 ; 4) ; (-3 ; -4)}.

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