a) x(x-y)-y(y-x)=x(x-y)+y(x-y)=(x+y)(x-y)=\(\left(\dfrac{-1}{2008}+\dfrac{-1}{2008}\right)\left(\dfrac{-1}{2008}+\dfrac{-1}{2008}\right)=\left(\dfrac{-1}{2008}+\dfrac{-1}{2008}\right).0=0\)
b) (x3 + x2 - 1). x - (x4 + x3 - x + 1)=(x4+x3-x)-(x4+x3-x+1)=x4+x3-x-x4-x3+x-1=-1
mik thấy đề hơi thừa, ko cần cho x, y cũng tính đc
Giải:
a) \(x.\left(x-y\right)-y.\left(y-x\right)\)
\(=\dfrac{-1}{2008}.\left(\dfrac{-1}{2008}-\dfrac{-1}{2008}\right)-\dfrac{-1}{2008}.\left(\dfrac{-1}{2008}-\dfrac{-1}{2008}\right)\)
\(=\dfrac{-1}{2008}.0-\dfrac{-1}{2008}.0\)
\(=0-0=0\)
b) \(\left(x^3+x^2-1\right).x-\left(x^4+x^3-x+1\right)\) (ko cần tính câu này)
\(=x^4+x^3-x-x^4-x^3+x-1\)
\(=\left(x^4-x^4\right)+\left(x^3-x^3\right)+\left(-x+x\right)+1\)
\(=0+0+0+1=1\)