If you have only two parameters and you know the influence of land use is more than the influence of slope and you can justify that in your analysis, then the equation is correct.
However, the only problem is that you cannot sum land use and slope directly even after assigning them weights because they have different units.
To apply weighted overlay analysis you need to standardize both land use and slope into a common scale, which means you should reclassify the pixel values of the two parameters using Reclassify Grid Values tool under SAGA tools in QGIS. There are many literatures about that in the internet you need to read about it. After reclassifying the old pixel values of both slope and land use parameters into new standard values, you can apply the equation in the raster calculator.