Explanation:
this is one of the formulas you should remember for life :
the general solution for a quadratic equation
ax² + bx + c = 0
is
x = (-b ± sqrt(b² - 4ac))/(2a)
in our case that is
x = (-4 ± sqrt(4² - 4×1×-1))/(2×1) = (-4 ± sqrt(16 + 4))/2 =
= (-4 ± sqrt(20))/2 = (-4 ± sqrt(4×5))/2 =
= (-4 ± 2×sqrt(5))/2 = -2 ± sqrt(5)
x1 = -2 + sqrt(5) = 0.236067977...
x2 = -2 - sqrt(5) = -4.236067977...
so, the negative solution is the x2 solution :
-4.236067977...
I don't know to how many decimal positions you are supposed to round. it is not specified in your problem definition.