The answer is:
[tex]f(3)=|x|+(-2x^{2})=-15[/tex]
Evaluating a function means replacing the variable with the given value (3 for this case).
To evaluate the function, we need to remember that the absolute value guarantees a possitive value, for example:
[tex]|-3|=3\\|-4|=4[/tex]
So, we are given the function:
[tex]f(x)=|x|+(-2x^{2})[/tex]
Then, evaluating we have:
[tex]f(3)=|3|+(-2*(3)^{2})=3+(-2*9)=3-18=-15[/tex]
Hence, the answer is:
[tex]f(3)=|x|+(-2x^{2})=-15[/tex]
Have a nice day!