10.
若\(a_{1} > 0\),\(a_{1}\neq 1\),\(a_{n+1}= \dfrac {2a_{n}}{1+a_{n}}(n=1,2,…)\)
\((1)\)求证:\(a_{n+1}\neq a_{n}\);
\((2)\)令\(a_{1}= \dfrac {1}{2}\),写出\(a_{2}\)、\(a_{3}\)、\(a_{4}\)、\(a_{5}\)的值,观察并归纳出这个数列的通项公式\(a_{n}\);
\((3)\)证明:存在不等于零的常数\(p\),使\(\{ \dfrac {a_{n}+P}{a_{n}}\}\)是等比数列,并求出公比\(q\)的值.