Bài 1:1: \(\left(x+1\right)\left(x^2-x+1\right)-\left(x^3-9\right)\) \(=x^3+1-x^3+9\) =1+9=102: \(x\left(x-1\right)^2-\left(x+2\right)\left(x^2-2x+4\right)\) \(=x\left(x^2-2x+1\right)-\left(x^3+8\right)\) \(=x^3-2x^2+x-x^3-8=-2x^2+x-8\) 3: \(\left(x+5\right)\left(x^2-5x+25\right)-\left(x+5\right)^3\) \(=x^3+5^3-\left(x^3+15x^2+75x+125\right)\) \(=x^3+125-x^3-15x^2-75x-125=-15x^2-75x\) Bài 2:a: \(A=\left(2x-1\right)\left(4x^2+2x+1\right)-7\cdot\left(x^3+1\right)\) \(=\left(2x\right)^3-1-7x^3-7=x^3-8\) b: Thay x=-1/2 vào A, ta được:\(A=\left(-\frac12\right)^3-8=-\frac18-8=-\frac{65}{8}\)Câu trả lời: Bài 1:1: \(\left(x+1\right)\left(x^2-x+1\right)-\left(x^3-9\right)\) \(=x^3+1-x^3+9\) =1+9=102: \(x\left(x-1\right)^2-\left(x+2\right)\left(x^2-2x+4\right)\) \(=x\left(x^2-2x+1\right)-\left(x^3+8\right)\) \(=x^3-2x^2+x-x^3-8=-2x^2+x-8\) 3: \(\left(x+5\right)\left(x^2-5x+25\right)-\left(x+5\right)^3\) \(=x^3+5^3-\left(x^3+15x^2+75x+125\right)\) \(=x^3+125-x^3-15x^2-75x-125=-15x^2-75x\) Bài 2:a: \(A=\left(2x-1\right)\left(4x^2+2x+1\right)-7\cdot\left(x^3+1\right)\) \(=\left(2x\right)^3-1-7x^3-7=x^3-8\) b: Thay x=-1/2 vào A, ta được:\(A=\left(-\frac12\right)^3-8=-\frac18-8=-\frac{65}{8}\)