Just a simple question #2

Given that x x and y y are real numbers not 0 0 , which satisfies this equation :

x y = x y = x y xy = \frac{x}{y}=x-y

What is the value of x + y = ? x+y=?


The answer is -1.5.

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2 solutions

Raven Herd
Jan 14, 2015

from the first two equations it is evident that y^2=1 so y=+/- 1 let this series be equal to k, then x=ky ,k+y these two values are equal checking the values of +1 and -1 we see that there is no solution at y=+1 so plugging values of-1 and then solve for x

Separate it as 2 equations :

x y = x y xy = \frac{x}{y} . . . . . . . . . . . . . . . . . 1

x y = x y xy = x - y . . . . . . . . . . . . 2

From the first equation, we can get the value of y y :

x y = x y xy = \frac{x}{y}

y = 1 y y = \frac{1}{y}

y 2 = 1 = > ( y = 1 ) y^2 = 1 => (y = 1) or ( y = 1 ) (y = -1)

From the second equation, we can get the value of x x

x y = x y xy = x - y

x y + y = x = > y ( x + 1 ) = x xy + y = x\ => y( x + 1 ) = x

  • when y = 1 y=1 then, 1 ( x + 1 ) = x = > x x = 1 1( x + 1 ) = x => x -x = -1 (undefined)

  • when y = 1 y=-1 then, 1 ( x + 1 ) = x = > 2 x = 1 -1( x + 1 ) = x => -2x = 1 y = 1 ; x = 1 2 \boxed{y = -1} ; \boxed{x = -\frac{1}{2}}

So, x + y = 3 2 = 1.5 x + y = -\frac{3}{2} = -1.5

Itb jalan-jalan

Eghar Anugrapaksi - 6 years, 4 months ago

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Haha iya, ini soal TO ITB, sama dengan yang Fisika itu

Andronikus Lumembang - 6 years, 4 months ago

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