Bonsoir
-5x²+21x = 4
-5x²+21-4 = 0
calcul du delta ( ou discriminant)
delta = b²-4ac = 21²-4(-5*-4) = 361
Vdelta (V veut dire racine)
Vdelta = V361 = 19
deux solutions
x' = (-b-Vdelta)/2a = (-21-19)/ 2*-5 = 4
x" = (-b+Vdelta)/2a = (-21+19)/ -10 = -2/-10= 0.2
