[tex]\displaystyle\bf\\f(x)=x^{2} +1\\\\1)\\\\f(5)=5^{2} +1=25+1=26\\\\\boxed{f(5)=26}\\\\2)\\\\f(x)=5\\\\5=x^{2} +1\\\\x^{2} =5-1=4\\\\\boxed{x_{1} =-2 \ \ ; \ \ x_{2} =2}[/tex]