\(1,\\ a,=a^2+2ab+b^2+a^2-2ab+b^2+a^2-b^2=3a^2+b^2\\ b,=a^2+8a+16+a^2-6a+9-2a^2-27=2a-2\\ c,=a^2-10a+25-a^2-8a-16-a+3=-19a+12\\ d,=a^3+3a^2+3a+1+a^3-6a^2+12a-8-2a^3-15a=-3a^2-7\)
\(2,\\ a,\Leftrightarrow x^2+6x+9-x^2+15=1\\ \Leftrightarrow6x=-23\Leftrightarrow x=-\dfrac{23}{6}\\ b,\Leftrightarrow x^2-10x+25+6x-x^2=-7\\ \Leftrightarrow-4x=-32\Leftrightarrow x=8\\ c,\Leftrightarrow1-x^2-x^2+8x-16=-15\\ \Leftrightarrow-2x^2+8x=0\\ \Leftrightarrow-2x\left(x-4\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x=4\end{matrix}\right.\\ d,\Leftrightarrow x^2+14x+49-x^2+36+6x=21\\ \Leftrightarrow20x=-64\Leftrightarrow x=-\dfrac{16}{5}\)
