Question 1203967
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y = 2x - 3
-6x + 3y = -9
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Second equation, {{{-2x+y=-3}}}


Substituting according to the first equation:  {{{-2x+2x-3=-3}}};
{{{0-3=-3}}}, which is true and the variables are lost.


LOOK at the system carefully!
{{{system(y=2x-3,-6x+3y=-9)}}}
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{{{system(y=2x-3,y=2x-3)}}}---------the two equations are equivalent.  All points on the one line are solutions.