x的2m-n次方=2,①x的2m+n次方=1②,①×②,x^(2m-n)*2^(2m+n)=2,x^(2m-n+2m+n)=2,即x^4m=2②÷①,得,x^(2m+n)*2^(2m-n)=1/2,x^(2m+n-2m+n)=1/2,即x^2n=1/2所以(x的四次方)m次方-（x²）的n次方=x^4m-x^2n=2-1/2=3...