Bài 1:
1) \(=x^2-2x-x^2+10+2x=10\)
2) \(=4x^2-9-4x^2-4x-1=-4x-10\)
3) \(=6x^2+33x-10x-55-6x^2-9x-14x-21=-76\)
Bài 2:
1) \(=3x^2y^2\left(x-2y+9\right)\)
2) \(=\left(x-y\right)\left(x+y\right)+2\left(x+y\right)=\left(x+y\right)\left(x-y+2\right)\)
3) \(x^2+x-2=\left(x^2-x\right)+\left(2x-2\right)=x\left(x-1\right)+2\left(x-1\right)=\left(x-1\right)\left(x+2\right)\)
Bài 3:
1) \(9-x^2=0\\ \Leftrightarrow\left(3-x\right)\left(3+x\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\)
2) \(\left(x+2\right)^2-\left(x+3\right)\left(x-3\right)=5\\ \Leftrightarrow x^2+4x+4-x^2+9=5\\ \Leftrightarrow4x=-8\\ \Leftrightarrow x=-2\)
3) \(\left(5-2x\right)\left(2x+7\right)=4x^2-25\\ \Leftrightarrow10x-4x^2+35-14x-4x^2+25=0\\ \Leftrightarrow-8x^2-4x+60=0\\ \Leftrightarrow2x^2+x-15=0\\ \Leftrightarrow\left(2x^2+6x\right)-\left(5x+15\right)=0\\ \Leftrightarrow2x\left(x+3\right)-5\left(x+3\right)=0\\ \Leftrightarrow\left(2x-5\right)\left(x+3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}\\x=-3\end{matrix}\right.\)
