Question 192870
2x - 3y = 5
-3y=-2x+5
y=-2x/-3+5/-3
y=2x/3-5/3 (red line)
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4x - 6y = 21 
-6y=-4x+21
y=-4x/-6+21/-6
y=2x/3-7/2 (green line)
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{{{ graph( 300, 200, -6, 5, -10, 10, 2x/3 -5/3 , 2x/3 -7/2) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions 2x/3 -5/3 and 2x/3 -7/2). 
Lines are parallel thus there is no unique (single solution) for x or y.