[tex]1)( x^{2} +6x+12)+(6x+6)= x^{2} +12x+18 \\
( x^{2} +6x+12)-(6x+6)= x^{2} +6
\\ ( x^{2} +6x+12)*(6x+6)=6x^3+42 x^{2} +108x+72 \\
2) \frac{25x^3}{15x+25x-35x} = \frac{25x^3}{5x}=5 x^{2} \\ 3)(x-a)(x+a) =x^{2} -225; x^{2} -a^2= x^{2} -225;a^2=225 \\ a=-15;sau:a=15 \\ 4)(a-b)(a+b)=40 \\ 4(a+b)=40 ;a+b=10 \\ 5)(4x+1)^2+(4x-4)(2x+3)+(x+3)^2=16 x^{2} +8x+1+8 x^{2} + \\ +4x-12+ x^{2} +6x+9=25 x^{2} +18x-2[/tex]
