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If a and b are positive integers for which ab-6a+5b=373, what is the minimal possible value of |a-b|?

 Oct 19, 2018
 #1
avatar
+1

I get a=44  and  b =13

So that: abs[44 - 13] =31

 Oct 19, 2018
 #2
avatar+343 
+1

Perfect will be a=b, because |ab|=>|aa|=0 so for a=b we have:

a26a+5a373=0 <=> a2a373=0

x=b±b24ac2a=> x=1±14(1)(373)2=>x=1±14932=> x=1± 38.632

x1=39.632=19.81

x2=37.632=18.81 BUT because is negative rejected 

so a=20 so 20b120+5b=373 => b=19.72 its NOT integers so you try values until a,b  integers

Finaly the answer is a=44  and  b =13 like Guest says and can see it in this graph if you try values! 

https://www.desmos.com/calculator/4fhytbda6x

Hope it helps!

 Oct 19, 2018
edited by Dimitristhym  Oct 19, 2018
 #3
avatar+283 
+1

Thank y'all both! :)

 Oct 19, 2018
 #4
avatar+130477 
+4

ab - 6a + 5b  =  373

 

We can write this as

 

ab - 6a + 5b  - 30  =  373 - 30

 

(a + 5 )  ( b - 6 )  =  373 - 30

 

(a + 5) (b - 6)  =  343

 

343  as a product of two factors  = 

 

1  * 343    or  343 * 1       

 

7 * 49    or   49 * 7

 

So....we have the following possibilities for a, b

 

a           b

338      7

2         55

44       13

 

So....   l a - b l    minimized  =  l 44 - 13 l  =  31

 

 

cool cool cool

 Oct 19, 2018

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