Easy!

If x , y x,y are non zero positive integers satisfying x y = x + y xy = x+y , what are the values of x x and y y ?

x = 3 , y = 2 x=3, y=2 x = 2 , y = 3 x=2, y=3 x = 1 , y = 3 x=1, y=3 x = 2 , y = 2 x=2, y=2

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13 solutions

Kenny Lau
Aug 15, 2015

x y = x + y \quad xy=x+y

x y x y = 0 \quad xy-x-y=0

By Simon's Favorite Factoring Trick ,

x y x y + 1 = 1 \quad xy-x-y+1=1

( x 1 ) ( y 1 ) = 1 \quad (x-1)(y-1)=1

{ x 1 = 1 y 1 = 1 \quad \begin{cases}x-1=1\\y-1=1\end{cases} or { x 1 = 1 y 1 = 1 \begin{cases}x-1=-1\\y-1=-1\end{cases}

{ x = 2 y = 2 \quad \begin{cases}x=2\\y=2\end{cases} or { x = 0 y = 0 \begin{cases}x=0\\y=0\end{cases} (rejected)

Uttkarsh Kohli
Aug 9, 2015

x=2,y=2 Because only 2 * 2=2+2

2 * 2=2+2

4=4 which is TRUE

PLEASE UPVOTE IF SATISFIED

Curtis Clement
Aug 14, 2015

It can be shown that ( x 1 ) ( 1 y ) = 1 \ (x-1)(1-y) = 1 and the integer solution follows.

it's (x-1)(y-1)=1.

Devin Ky - 5 years, 10 months ago
Katie Mor
Aug 10, 2015

2 is the only non-zero integer which produces the same result when added together and when multiplied by itself. 2 × 2 2 \times 2 = 4 4 , 2 + 2 2 + 2 = 4 = 4 So both X and Y must be 2.

Wilson Widyadhana
Sep 11, 2015

Since xy=x+y The only number which satisfies this is 2.

Tushar Kaushik
Sep 9, 2015

Just put the values

Himanshu Sharma
Sep 4, 2015

There is no need to give options.due to this just put the values and find and.

Yash Sharma
Sep 3, 2015

Sec^2theta = X Csc^2theta = Y Now say ??

Avi Sihag
Aug 30, 2015

As 2x2 and 2+2 are equal and hence satisfy x+y=xy ,we get the answer as x=2 and y=2.

Venkatesh Patil
Aug 29, 2015

From the given options, the only option that satisfies the given condition (that is multiplication and addition are equal) is the value of x and y is 2. Hence the proof.

Senthamil Arasi
Aug 20, 2015

xy=x+y x=2 y=2

2*2=2+2

4=4 so the answer is x^2y^2=(xy)^2 x=2, y=2

Hadia Qadir
Aug 18, 2015

both are 2... and nothing have not the same result as 2 when it is: x + y x * y x ^ y

Tin Tun Naing
Aug 15, 2015

NOT a solution. Just an observation. xy=x+y ==> y = x/(x-1) Now take derivative respect to x. y' = -1/(x-1)^2 ==> at x = 1 there is vertical asymptote and no global minimum and maximum values are found.

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