3.
正数数列\(\left\{{a}_{n}\right\} \)、\(\left\{{b}_{n}\right\} \)满足:\({a}_{1}\geqslant {b}_{1} \),且对一切\(k\geqslant 2,k∈{N}^{*} \),\({a}_{k} \)是\({a}_{k-1} \)与\({b}_{k-1} \)的等差中项,\({b}_{k} \)是\({a}_{k-1} \)与\({b}_{k-1} \)的等比中项.
\((1)\)若\({a}_{2}=2,{b}_{2}=1 \),求\({a}_{1},{b}_{1} \)的值;
\((2)\)求证:\(\left\{{a}_{n}\right\} \)是等差数列的充要条件是\(\left\{{a}_{n}\right\} \)为常数数列;
\((3)\)记\({c}_{n}=\left|{a}_{n}-{b}_{n}\right| \),当\(n\geqslant 2\left(n∈{N}^{*}\right) \)时,指出\({c}_{2}+⋯+{c}_{n} \)与\({c}_{1} \)的大小关系并说明理由.