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Q. Solve the following pair of linear equations by the substitution method.

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3x

–

y

= 3 ;

9x

–

3y

= 9

Soln.

y + 3

3

x =

9x

–

3y

= 9

... (ii)

... (iii)

Substituting equation (iii) in equation (ii) ;

y + 3

3

9

–

3y

= 9

–

3y

= 9

3y

= 9

9

Since both the variables get cancelled on solving.

These equations do not have a unique solution

3x

–

y

= 3

... (i)

Write this equation either �x = something

or

y = something

3

+ 9

Consider (i)

Consider any one of the two equations