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x in (-oo:+oo)
((-x)^2)/40+(31*x)/40+4/5 = y // - y
((-x)^2)/40+(31*x)/40-y+4/5 = 0
1/40*x^2+31/40*x-y+4/5 = 0
DELTA = (31/40)^2-(1/40*4*(4/5-y))
DELTA = 961/1600-1/10*(4/5-y)
961/1600-1/10*(4/5-y) = 0
(-1/10*1600*(4/5-y))/1600+961/1600 = 0
961-1/10*1600*(4/5-y) = 0
160*y+833 = 0
(160*y+833)/1600 = 0
(160*y+833)/1600 = 0 // * 1600
160*y+833 = 0
160*y+833 = 0 // - 833
160*y = -833 // : 160
y = -833/160
DELTA = 0 <=> t_1 = -833/160
x = -31/40/(1/40*2) i y = -833/160
x = -31/2 i y = -833/160
( x = ((961/1600-1/10*(4/5-y))^(1/2)-31/40)/(1/40*2) or x = (-(961/1600-1/10*(4/5-y))^(1/2)-31/40)/(1/40*2) ) i y > -833/160
( x = 20*((961/1600-1/10*(4/5-y))^(1/2)-31/40) or x = -20*((961/1600-1/10*(4/5-y))^(1/2)+31/40) ) i y > -833/160
y-(-833/160) > 0
y+833/160 > 0
y+833/160 > 0 // - 833/160
y > -833/160
x in { -31/2, 20*((961/1600-1/10*(4/5-y))^(1/2)-31/40), -20*((961/1600-1/10*(4/5-y))^(1/2)+31/40) }
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