Equation : 40y(au carre)+48y-64=0

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)