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Meilleure réponse !
2014-05-14T21:48:48+02:00
Bonsoir
40y² +  48y - 64 = 0
delta = b²-4ac = (48)² -4(40)(-64) = 2304 + 10240 = 12544 
Vdelta = V12544 = 112 
deux solutions
x ' = (-b - Vdelta)/2a = (-48-112) / 80 = -2
x" = (-b + Vdelta)/2a = (-48 + 112)/80 = 0.8
soit
40y² + 48y - 64 = (40y - 32)(y + 2)