And the first function that I wanna test, let's say I have f of x is equal to two x. Is this a solution to this differential equation? Pause the video again and see if you can figure it out. Well, to figure that out, you have to say, well, what is f prime of x? F prime of x is just going to be equal to two. And then test the equality. Is two, is f prime of x equal to f of x, which is two x, minus x, minus x.