Question

   Solve the following equations by substitution method 1/x+2/y=9;2/x+1/y=12 [x≠0,y≠0]

Answer 1

1/x+2/y=9 multiply with 2
2/x+4/y=18 ,2/x+1/y=12
subtract the two
2/x+4/y-2/x-1/y=18-12
4/y-1/y=6
y=1/2
x=1/5

Answer 2

1/x = a     1/y = b

       a + 2 b = 9            so a = 9 - 2b  --- eq 1

        2 a + b = 12   
substitute the value of a from equation 1,
  
      2 (9 - 2b) + b = 12
   18 - 4 b +b = 12
           3 b = 6          b = 2
        a = 9 - 2b = 5

so x = 1/5      y = 1/2