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x in (-oo:+oo)
x^2-((20/2)*x^2)-x-(7*x)-15 = 0
x^2-10*x^2-x-7*x-15 = 0
-9*x^2-8*x-15 = 0
DELTA = (-8)^2-(-15*(-9)*4)
DELTA = -476
DELTA < 0
x belongs to the empty set
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