The moment of inertia (MOI) for a rectangular plate inclined at an angle can be calculated by projecting the plate onto a plane perpendicular to the axis of rotation and then using standard techniques to find the MOI of that projection. Displacing components parallel to the axis does not affect the MOI, allowing for direct integration methods. It's important to note that the axis of rotation may not be a principal axis, which can lead to incorrect results when calculating angular momentum. The formula I = Ixxcos^2(theta) + Iyy sin^2(theta) applies when the product of inertia is zero. Proper understanding of these principles is essential for accurate calculations in rotational dynamics.