[tex]S_n=a_1*\frac{1-q^n}{1-q}\\\\242=2*\frac{1-3^n}{1-3}\\\\121=\frac{1-3^n}{-2}\\\\1-3^n=-242\\\\-3^n=-243\\\\3^n=243\\\\3^n=3^5\rightarrow n=5\\\\a_n=a_1*q^{n-1}\\\\a_n=2*3^{n-1}\\\\[/tex]
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[tex]S_n=a_1*\frac{1-q^n}{1-q}\\\\242=2*\frac{1-3^n}{1-3}\\\\121=\frac{1-3^n}{-2}\\\\1-3^n=-242\\\\-3^n=-243\\\\3^n=243\\\\3^n=3^5\rightarrow n=5\\\\a_n=a_1*q^{n-1}\\\\a_n=2*3^{n-1}\\\\[/tex]