Another solve by elimination: -x + 3y = 6, x - 9y = 9

[Guest]

-x + 3y = 6
x - 9y = 9

-6y = 15
y = -15/6

-x + 3(-15/6) = 6
-x-(15/2) = 6
-x = (12/2) + (15/2)
x = -27/2

Is this correct if doing by elimination?
Thanks!!
Andrea

 

[minestrone]

Yepp. your answer is correct
personally, i like to number the two equations and then explain what i'm doing


-x + 3y = 6 ( 1 )
x - 9y = 9 ( 2 )

( 1 ) + ( 2 )
-6y = 15
y = -15/6

Substituting y=-15/6 into ( 1 )
-x + 3(-15/6) = 6
-x-(15/2) = 6
-x = (12/2) + (15/2)
x = -27/2