\(1,\\ a,=5x^2+15x+8x-80-4x=5x^2+19x-80\\ b,=2x^2-5x-12-4x^2-8x+3=-2x^2-13x-9\\ c,=4x^2-12x+9+x^2-16-15=5x^2-12x-22\\ d,=25x^2+30x+9-x^2+9-6x+8=24x^2+24x+26\\ 2,\\ a,\Rightarrow17x-2x^2-21+2x^2+2x-8=0\\ \Rightarrow19x=-29\Rightarrow x=-\dfrac{29}{19}\\ b,\Rightarrow4x^2-4x-14x-3x^2+5-x^2+10=0\\ \Rightarrow-18x=-15\\ \Rightarrow x=\dfrac{5}{6}\)
\(c,\Rightarrow\left[{}\begin{matrix}x=10\\x=-\dfrac{1}{2}\end{matrix}\right.\\ d,\Rightarrow\left(5x-x+3\right)\left(5x+x-3\right)=0\\ \Rightarrow\left[{}\begin{matrix}4x=-3\\6x=3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-\dfrac{3}{4}\\x=\dfrac{1}{2}\end{matrix}\right.\)
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