8.
定义:在数列\(\left\{ a_{n} \right\}\)中,若\(a_{n}^{2}{-}a_{n{-}1}^{2}{=}p(n{\geqslant }2{,}n{∈}N^{{+}}{,}p\)为常数\()\)则称\(\left\{ a_{n} \right\}\)为“等方差数列”,下列是对“等方差数列”的有关判断,
其中正确命题的个数为( ) \(①\)若\(\left\{ a_{n} \right\}\)
是“等方差数列”,在数列\(\left\{ \dfrac{1}{a_{n}} \right\}\)
是等差数列; \(②\)\(\left\{ {({-}2)}^{n} \right\}\)
是“等方差数列”; \(③\)若\(\left\{ a_{n} \right\}\)
是“等方差数列”,则数列\(\left\{ a_{{kn}} \right\}(k{∈}N^{{+}}{,}k\)
为常\()\)也是“等方差数列”; \(④\)若\(\left\{ a_{n} \right\}\)既是“等方差数列”又是等差数列,则该数列是常数数列.