[tex]Zadanie\ 5\\\\a_1=1\\r=2\\\\S_{n}=\frac{2a_1+(n-1)r}{2}\cdot n\\\\S_{n}=\frac{2\cdot1+(n-1)\cdot2}{2}\cdot n=\frac{2+2n-2}{2}\cdot n=\frac{2n^{2} }{2}=n^{2}[/tex]
