Sunday, February 23, 2014

Solve the simultaneous equations x^2+xy+y^2=200 x+(xy)^(1/2)+y=20

x^2 + xy + y62 =
200...............(1)


x + (xy)^1/2 + y =
20...............(2)


First we will re-wrtie equation
(2).


We will move (xy)^1/2 to the right
sides.


==> (x+ y) = 20 -
(xy)^1/2


Now we will square both
sides.


==> (x+ y)^2 = (20- (xy)^1/2)
^2


==> x^2 = 2xy + y62 = 400 - 40(xy)^1/2)
+xy


Now subtract xy from both
sides.


==> x^2 + xy + y^2 = 400 -
40(xy)^1/2)


But, from equation (1) , we know that x^2 + xy
+ y^2 = 200.


==> 200 = 400 -
40(xy)^1/2)


==> -200 =
-40(xy)^1/2


==> (xy)^1/2 = 200/40 =
5


==> xy =
25.............(3)


Now we will substitute in
(1) and (2).


==> x^2 + y^2 + 25 =
200


==> x^2 = y^2 = 175
............(4)


==> x+ 5 + y
20


==> x+ y =
15


==> y= 15-x
...............(5)


Now substitute on
(3)


==> x*y =
25


==> x( 15-x) =
25


==> 15x -x^2 =
25


==> x^2 - 15x + 25 =
0


==> x1=( 15+ 5sqrt5)/2  ==>
y1= ( 15-5sqrt5)/2


==>
x2= (15-5sqrt5) /2 ==> y2= (15+5sqrt5)/2

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