7.
已知数列\(\{a_{n}\}\),设\(\triangle a_{n}=a_{n+1}-a_{n}(n=1,2,3,…)\),若数列\(\{\triangle a_{n}\}\)为单调增数列或常数列时,则\(\{a_{n}\}\)为凸数列.
\((\)Ⅰ\()\)判断首项\(a_{1} > 0\),公比\(q > 0\),且\(q\neq 1\)的等比数列\(\{a_{n}\}\)是否为凸数列,并说明理由;
\((\)Ⅱ\()\)若\(\{a_{n}\}\)为凸数列,求证:对任意的\(1\leqslant k < m < n\),且\(k\),\(m\),\(n∈N\),均有\( \dfrac {a_{n}-a_{m}}{n-m}\geqslant a_{m+1}-a_{m}\geqslant \dfrac {a_{m}-a_{k}}{m-k}\),且\(a_{m}\leqslant max\{a_{1},a_{n}\}\);其中\(max\{a_{1},a_{n}\}\)表示\(a_{1}\),\(a_{n}\)中较大的数;
\((\)Ⅲ\()\)若\(\{a_{n}\}\)为凸数列,且存在\(t(1 < t < n,t∈N)\),使得\(a_{0}\leqslant a_{t}\),\(a_{n}\leqslant a_{t}\),求证:\(a_{1}=a_{2}=…=a_{n}\).