Помогите с алгеброй

(m+1)x^2 + 2mx - 5 + m = 0
(m+1)*x^2 + 2m*x - (5 - m) = 0

ax^2 + bx + c = 0
x(1,2) = [ - b + - V(b^2 - 4*a*c)] / 2a

В задании:
a = (m+1)
b = 2m
c = (5-m)
=>
x(1,2) = [- 2m + - V((2m)^2 - 4*(m+1)*(-(5-m))] / 2*(m+1)

Единственный корень уравнения будет при D = 0 =>
V((2m)^2 - 4*(m+1)*(-(5-m)) = 0
4m^2 - (4m+4)(m-5) = 0
4m^2 - 4m^2 - 4m + 20m + 20 = 0
16m = - 20
m = - 5/4