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(2/5)*(15*x-(30*y)) = 0
(2/5)*(15*x-30*y) = 0
2/5*(15*x-30*y) = 0
( 15*x-30*y )
15*x-30*y = 0 // + -30*y
15*x = -(-30*y) // : 15
x = (-(-30*y))/15
x = 2*y
( 2/5 )
2/5 = 0
x belongs to the empty set
x = 2*y
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