a) Sai đề hay sao ý ạ!
b) \(16x^2-\left(x^2+4\right)^2=\left(4x\right)^2-\left(x^2+4\right)^2\)
\(=\left(x^2+4x+4\right)\left(4x-x^2-4\right)\)
c) Đặt x + y = a; x - y = b suy ra a + b = 2x
Ta có \(a^3+b^3=\left(a+b\right)\left(a^2-ab+b^2\right)\)
\(=2x\left[\left(a+b\right)^2-3ab\right]\)
\(=2x\left[4x^2-3\left(x+y\right)\left(x-y\right)\right]=2x\left(x^2+3y^2\right)\)