\(\left[\dfrac{1}{2}-\left(x+3\right)^2\right]:\dfrac{5}{4}=-2,8\)
=>\(\dfrac{1}{2}-\left(x+3\right)^2=-2,8\cdot\dfrac{5}{4}=-3,5\)
=>\(\left(x+3\right)^2=\dfrac{1}{2}+\dfrac{7}{2}=4\)
=>\(\left[{}\begin{matrix}x+3=2\\x+3=-2\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=-1\\x=-5\end{matrix}\right.\)