-4x² + 20x - 25 = 0 The discriminant Δ = b² - 4.a.c, where a= -4; b= 20 & c = - 25 Then Δ = (20)² - 4(-4)(-25) Δ = 0 , since the discriminant = 0, we have one real solution (answer B)
For more info about Δ, If : Δ > 0, then there are 2 real solutions, x' and x"
Δ = 0, then there are 2 equal real solutions, x' = x"
Δ < 0, then there are no solutions, or 2 imaginary values of x' and x"