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x in (-oo:+oo)
y = (2/9)*(x-3)*(x-15) // - (2/9)*(x-3)*(x-15)
y-((2/9)*(x-3)*(x-15)) = 0
(-2/9)*(x-3)*(x-15)+y = 0
y-2/9*(x-3)*(x-15) = 0
y-2/9*(x-3)*(x-15) = 0
4*x-2/9*x^2+y-10 = 0
4*x-2/9*x^2+y-10 = 0
4*x-2/9*x^2+y-10 = 0
DELTA = 4^2-(-2/9*4*(y-10))
DELTA = 8/9*(y-10)+16
8/9*(y-10)+16 = 0
8/9*(y-10)+16 = 0
8/9*y+64/9 = 0
8/9*y+64/9 = 0
8/9*y+64/9 = 0 // - 64/9
8/9*y = -64/9 // : 8/9
y = -64/9/8/9
y = -8
DELTA = 0 <=> t_3 = -8
x = -4/(-2/9*2) i y = -8
x = 9 i y = -8
( x = ((8/9*(y-10)+16)^(1/2)-4)/(-2/9*2) or x = (-(8/9*(y-10)+16)^(1/2)-4)/(-2/9*2) ) i y > -8
( x = -9/4*((8/9*(y-10)+16)^(1/2)-4) or x = 9/4*((8/9*(y-10)+16)^(1/2)+4) ) i y > -8
y+8 > 0
y+8 > 0 // - 8
y > -8
x in { 9, -9/4*((8/9*(y-10)+16)^(1/2)-4), 9/4*((8/9*(y-10)+16)^(1/2)+4) }
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