注意是计算,不是因式分解：

①(-3)^(n+1)÷[3×(-3)^n]
=(-3)^(n+1)÷(-3)^(n+1)
=1
②(x^2-y^2)^3
=x^6-3x^4y^2+3x^2y^4-y^6
③√[(x+3/x)^2-(x-3/x)^2]
=√(6/x*2x)
=√12
=2√3