8x²-2x-15 = 0
a=8
b=-2
c=-15
∆ = b²-4ac
∆= 4 - 8 ×(-15) ×4
∆= 4+ 480
∆ = 484 => x1 = -b + √∆/2a =>
=> x1= 2+22/2×8 = 24/16=3/2
√∆ = 22
X2=-b-√∆/2a = 2-22/2×8 = -20/16 = - 5/4
8x²-2x-15 = a(x-x1)(x-x2) = 8( x- 3/2 )( X+ 5/4) = 0
=> 2 (x-3/2) × 4( X+5/4 ) = 0
=> (2x-3) × ( 4x +5) = 0 => odată 2x-3 = 0 => X= 3/2
si 4x+5 = 0 => X= -5/4
x€ { 3/2; -5/4}
