đề bài đây ảnh lỗi mình ko gửi được
1) cho x+y=1.tính (x-y).(x2+y2).(x4+y4)-x8-y8+1
Ta có: \(\left(x-y\right)\left(x^2+y^2\right)\left(x^4+y^4\right)-x^8-y^8+1\)
\(=\left(x-y\right)\left(x+y\right)\left(x^2+y^2\right)\left(x^4+y^4\right)-x^8-y^8+1\)
\(=\left(x^2-y^2\right)\left(x^2+y^2\right)\left(x^4+y^4\right)-x^8-y^8+1\)
\(=\left(x^4-y^4\right)\left(x^4+y^4\right)-x^8-y^8-1\)
\(=x^8-y^8-y^8-x^8-1\)
\(=-2y^8-1\)

