Question

2x+3y=9 4x+6y=18 solve this equation by using substitution method

Answer 1

2x=9-3y
x=9-3y/2
put x=9-3y/2 in 4x+6y=18
4 (9-3y/2)+6y=18
18-6y+6y=18
18=18
not valid ans

Answer 2

Given :  2x+3y=9 4x+6y=18  

To find : solve this equation by using substitution method

Solution:

2x+3y=9   Eq1

4x+6y=18  Eq2

Dividing Eq 2 by 2

we get

2x + 3y = 9  same as  Eq 1

Hence both are the same equations

Hence infinite solution

Using substitution method

2x+3y=9   Eq1

=> 2x = 9 - 3y

=> x = (9 - 3y)/2

Substituting in Eq 2

4x+6y=18

=> 4((9 - 3y)/2) + 6y = 18

=> 2 (9 - 3y) + 6y = 18

=> 18 - 6y + 6y = 18

=>  18 = 18  

independent of   y  

Hence infinite solutions

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