Ta có :
\(A=3\left(x-1\right)^2-\left(x+1\right)^2+2\left(x-3\right)\left(x+3\right)-\left(2x+3\right)^2-\left(5-20x\right)\)
\(=3x^2-6x+3-x^2+2x-1+2x^2-18-4x^2-12x-9-5+20x\)
\(=\left(3x^2-x^2+2x^2-4x^2\right)-\left(6x+2x+12x-20x\right)+\left(3-1-18-5-9\right)\)
\(=-30\) không phụ thuộc vào biến \(x\)
Ta có: \(A=3\left(x-1\right)^2-\left(x-1\right)^2+2\left(x-3\right)\left(x+3\right)-\left(2x+3\right)^2-\left(5-20x\right)\)
\(=3\left(x^2-2x+1\right)-\left(x^2-2x+1\right)+2\left(x^2-9\right)-\left(4x^2+12x+9\right)-5+20x\)
\(=3x^2-6x+3-x^2+2x-1+2x^2-18-4x^2-12x-9-5+20x\)
=4x-30
Sai đề rồi bạn