Đáp án:
$2)b)(23x+6)(18-7x)\\ 3)b)\text{Vô nghiệm}.$
Giải thích các bước giải:
$2)\\ b)16(2x+3)^2-9(5x-2)^2\\ =4^2(2x+3)^2-3^2(5x-2)^2\\ =(4(2x+3))^2-(3(5x-2))^2\\ =(8x+12)^2-(15x-6)^2\\ =(8x+12+15x-6)(8x+12-15x+6)\\ =(23x+6)(18-7x)\\ 3)\\ b)(x+2)^3-x^2(x-6)=4\\ \Leftrightarrow x^3 + 6 x^2 + 12 x + 8-x^3+6x^2-4=0\\ \Leftrightarrow 12x^2 + 12 x+4=0\\ \Leftrightarrow x^2 + x+\dfrac{1}{3}=0\ \Leftrightarrow x^2 + x+\dfrac{1}{4}+\dfrac{1}{12}=0\\\ \Leftrightarrow \left( x+\dfrac{1}{2}\right)^2+\dfrac{1}{12}=0(\text{Vô nghiệm}).$
