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