(规律探究题)计算:(1)(√2+1)(√2-1)=1,(2)(√3+√2)(√3-√2)=1,(3)(2+√3)(2-√3)=1,(4)(√5+2)(√5-2)=1.通过以上计算,观察规律,写出用含n(n为正整数)的式子表示上面规律的等式.