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Attributed to Ramanujan (Posted on 2022-03-26) Difficulty: 2 of 5
Given:

x+ sqrt(y)=7
sqrt(x)+y =11

Solve for integer values of x & y, formally, neither by guessing nor software.

Assume that x is less than y.

No Solution Yet Submitted by Ady TZIDON    
Rating: 4.0000 (1 votes)

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Solution Puzzle Solution Comment 3 of 3 |
Since, (vx, vy)=(11-y, 7-x), it follows that each of vx and vy is an integer.
Now, subtracting  the first equation from the second, we obtain:
y-x-(vy-vx)=4
=> (vy-vx)(vy+vx-1)= 4
Since, y>x, it follows that vy> vx
Also, (vy-vx) and (vy+vx-1) must possess different parity.
Then, we must have:
(vy-vx)(vy+vx-1)=1*4, 4*1
=> (vy, vx)=(3,-1), (3,2)
If (vy,vx)=(3,-1)=>(y,x)=(9,1)
Then, x+vy=1+3=4<7. This is a contradiction 
If (vy,vx)=(3,2)=> (y,x) =(9,4)
It can easily be verified that (x,y)=(4,9) satisfies each of the given equation s.
Consequently,  (x,y)=(4,9) is the only possible solution to the given problem.

Edited on March 26, 2022, 1:14 pm
  Posted by K Sengupta on 2022-03-26 13:12:14

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