If 9x-3y=12 and 3x-5y=7 then 6x-2y =?A. -5B.  4C.  2D.  8

D

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Deepa Thomas

  • Nov 15th, 2012
 

9x-3y=12 --> eq.①
3x-5y=7 --> eq.② (x-3)
(multiply eq.② by -3):
-9x+15y= -21 --> eq.③
9x-3y=12 -->eq.①
-9x+15y=-21 --> eq.③
[9x-9x (cancel)]
-3y+15y= 12-21
12y=-9
y= -3/4
Replace y by (-3/4) in eq.①:
9x-3(-3/4)= 12
9x+9/4=12
9x=12-9/4
9x=39/4
x= 13/12
x=-13/12
y=-3/4
When x= 13/12 and y=-3/4
6(13/12) - 2(-3/4)= 8
ans D

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