[tex]f(a+h)=(a+h)^2+3(a+h)+5\\\\f(a+h)=a^2+2ah+h^2+3a+3h+5\\\\[/tex]
[tex]\bf f(x)=x^2+3x+5~~ \begin{cases}f(a+h)\\x=a+h\end{cases}\implies f(a+h)=(a+h)^2+3(a+h)+5\\\\\\f(a+h)=(a^2+2ah+h^2)+(3a+3h)+5\\\\\\f(a+h)=a^2+2ah+h^2+3a+3h+5[/tex]
