Consider the function $f(x)=-x^2+5$
Use it to find $f(4),f(-3)$, and $f(a-3)$

Step 1 ：First, we need to understand the function $f(x)=-x^2+5$. This is a quadratic function, where $x$ is the variable, and $-x^2+5$ is the expression that gives the value of the function for any given $x$.

Step 2 ：To find $f(4)$, we substitute $x=4$ into the function: $f(4)=-4^2+5=-16+5=-11$.

Step 3 ：To find $f(-3)$, we substitute $x=-3$ into the function: $f(-3)=-(-3{)}^2+5=-9+5=-4$.

Step 4 ：To find $f(a-3)$, we substitute $x=a-3$ into the function: $f(a-3)=-(a-3{)}^2+5=-(a^2-6a+9)+5=-a^2+6a-4$.

Step 5 ：So, $f(4)=-11$, $f(-3)=-4$, and $f(a-3)=-a^2+6a-4$.

Step 6 ：We can check our results by substituting the values back into the original function and verifying that they satisfy the equation.

Step 7 ：The final results are in their simplest form, and they meet the requirements of the problem.