$$\sqrt{- x^{2} + 2 x + 3} + 0 = 0$$
transform
$$- x^{2} + 2 x + 3 = 0$$
This equation is of the form
$$a*x^2 + b*x + c = 0$$
A quadratic equation can be solved using the discriminant
The roots of the quadratic equation:
$$x_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where $D = b^2 - 4 a c$ is the discriminant.
Because
$$a = -1$$
$$b = 2$$
$$c = 3$$
, then
$$D = b^2 - 4 * a * c = $$
$$2^{2} - \left(-1\right) 4 \cdot 3 = 16$$
Because D > 0, then the equation has two roots.
$$x_1 = \frac{(-b + \sqrt{D})}{2 a}$$
$$x_2 = \frac{(-b - \sqrt{D})}{2 a}$$
or
$$x_{1} = -1$$
Simplify$$x_{2} = 3$$
Simplify