a)(2x+3)²-2(2x+3)(2x-5)+(2x-5)²=x^2+6x+64
(=)(2x+3-2x+5)²( đây là hằng đẳng thức (a-b)²)=X²+6X+64
(=)8²=x²+6x+64
(=)64=x²+6x+64
(=)64-x²-6x-64=0
(=)-x²-6x=0
(=)-x(x-6)=0
(=)\(\left[ \begin{array}{l}-x=0\\x-6=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=0\\x=6\end{array} \right.\)
b)(x^4+2x^3+10x-25):(x^2+5)=3
(=)x²+2x-5=3
(=)x²+2x-5-3=0
(=)x²+2x-8=0
(=)x²-2x+4x-8=0
(=)x(x-2)+4(x-2)=0
(=)(x+4)(x-2)=0
(=)\(\left[ \begin{array}{l}x+4=0\\x-2=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=-4\\x=2\end{array} \right.\)
