7.
设正项数列\(\left\{{a}_{n}\right\} \)的前\(n\)项和为\({S}_{n} \),且满足\({S}_{n}= \dfrac{1}{2}{{a}_{n}}^{2}+ \dfrac{n}{2}\left(n∈N*\right) \).
\((1)\)计算\({a}_{1}\;,\;{a}_{2\;},\;{a}_{3} \)的值,并猜想\(\left\{{a}_{n}\right\} \)的通项公式;
\((2)\)用数学归纳法证明\(\left\{{a}_{n}\right\} \)的通项公式.