(I just figured out I can use that "LaTeX" thing)

\(f(x)=2x^2-5x\)

Using ↑↑↑↑ that function up there

\( f(2x)-2f(x)\)

So, you want me to find f(2x)-2f(x), huh?

In the above equation, you can just plug in 2x, which yields:

2(2x)^2-5(2x) = 8x^2 - 10x

Now we find 2f(x), which is just 2(2x^2-5x) = 4x^2 - 10x

subtracting 4x^2 - 10x from 8x^2 - 10x, we get 4x^2.

Congratulations on figuring out some latex!!