\(-\left(x+5\right)^2-\left(x-3\right)^2\\ =-\left(x^2+10x+25\right)-\left(x^2-6x+9\right)\\ =-x^2-10x-25-x^2+6x-9\\ =-2x^2-4x-34\)
\(-\left(x+5\right)^2-\left(x-3\right)^2\)
\(=-\left[\left(x+5\right)^2+\left(x-3\right)^2\right]\)
\(=-\left(x^2+10x+25+x^2-6x+9\right)\)
\(=-\left(2x^2+4x+34\right)\)