[tex]\displaystyle\bf\\2)\\\\4xy+7x^{2} =x\cdot(4y+7x)\\\\7d^{2}-21d^{4} =7d^{2} -7d^{2} \cdot 3d^{2} =7d^{2}\cdot(1-3d^{2})\\\\7a-7b+a^{2} -ab=(7a-7b)+(a^{2} -ab)=\\\\=7\cdot(a-b)+a\cdot(a-b)=(a-b)\cdot(7+a)\\\\\\3)\\\\6x^{2}-9x=0 \ |:3\\\\2x^{2} -3x=0\\\\x\cdot(2x-3)=0\\\\\\\left[\begin{array}{ccc}x=0\\2x-3=0\end{array}\right\\\\\\\left[\begin{array}{ccc}x_{1} =0\\x_{2} =1,5\end{array}\right\\\\\\Otvet \ : \ 0 \ \ ; \ \ 1,5[/tex]
[tex]\displaystyle\bf\\4)\\\\x^{3} -(x^{2} -3x)(x+3)=x^{3} -(x^{3} +\underbrace{3x^{2} -3x^{2}}_{0} -9x)=\\\\=x^{3} -x^{3} +9x=9x\\\\\\5)\\\\12-x(x-3)=(6-x)(x+2)\\\\12-x^{2} +3x=6x+12-x^{2} -2x\\\\12-x^{2} +3x=4x+12-x^{2} \\\\-x^{2} +3x-4x+x^{2} =12-12\\\\-x=0\\\\Otvet \ : \ x=0[/tex]
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[tex]\displaystyle\bf\\2)\\\\4xy+7x^{2} =x\cdot(4y+7x)\\\\7d^{2}-21d^{4} =7d^{2} -7d^{2} \cdot 3d^{2} =7d^{2}\cdot(1-3d^{2})\\\\7a-7b+a^{2} -ab=(7a-7b)+(a^{2} -ab)=\\\\=7\cdot(a-b)+a\cdot(a-b)=(a-b)\cdot(7+a)\\\\\\3)\\\\6x^{2}-9x=0 \ |:3\\\\2x^{2} -3x=0\\\\x\cdot(2x-3)=0\\\\\\\left[\begin{array}{ccc}x=0\\2x-3=0\end{array}\right\\\\\\\left[\begin{array}{ccc}x_{1} =0\\x_{2} =1,5\end{array}\right\\\\\\Otvet \ : \ 0 \ \ ; \ \ 1,5[/tex]
[tex]\displaystyle\bf\\4)\\\\x^{3} -(x^{2} -3x)(x+3)=x^{3} -(x^{3} +\underbrace{3x^{2} -3x^{2}}_{0} -9x)=\\\\=x^{3} -x^{3} +9x=9x\\\\\\5)\\\\12-x(x-3)=(6-x)(x+2)\\\\12-x^{2} +3x=6x+12-x^{2} -2x\\\\12-x^{2} +3x=4x+12-x^{2} \\\\-x^{2} +3x-4x+x^{2} =12-12\\\\-x=0\\\\Otvet \ : \ x=0[/tex]