Question 925217
let numbers be x, y
 so   {{{x+y= 13}}}
       {{{ x^2-y^2 =39}}}
Formulae:  {{{ a^2-b^2 = (a+b)*(a-b)}}}
      {{{ (x+y)*(x-y) =39}}}
       put x+y= 13 in above equation
       {{{ 13*(x-y) =39}}}
        divide with 13 on both sides
          {{{ 13*(x-y)/13 =39/13}}}
               {{{x-y= 3}}}
      but x+y= 13  adding above equations
                x-y= 3
                x+y= 13
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             2x  = 16
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2x=16
divide with 2 on both sides
      {{{ 2x/2 = 16/2}}}
            x=8
 put x= 8 in x-y =3
              8-y =3
             move -y to the right
             8=y+3 
     move 3  to the left
               8-3  = y
            5= y
so y= 5
  result : x=8 , y=5