D3dx9.dll is a dynamically connected library that serves as an auxiliary component for many games and programs working with multimedia content. Its absence on the computer leads to impossibility of program work. In such cases, such messages appear:
"It is not possible to start the program because there is no d3dx9.dll on the computer. Try reinstalling the program."
"This application has failed to start because d3dx9.dll was not found. Re-installing the application may fix this problem."
There are two solutions to the problem: reinstall DirectX, or manually download a DLL file and copy it to the right folder. If DirectX is not installed in the system at all, the only solution is to install it (as other libraries included in it will also be needed for the game). By clicking on the "Download" button you will see all download options, including a separate DLL file. If you still want to put it into the system manually, you will find instructions in the file archive that will help you to do this. For your information: DirectX is the Windows component responsible for processing and output of video and sound. The process of creating games and multimedia applications is greatly facilitated, so developers use it almost always. Often this library package comes with the games.