Ex. 15.4, Q. No. 3, (i)
The statement should be true.
If we would put the source facing to any corner of the cube, it will produce a rectangular shadow. ????

Dear student,
Here the statement is not completely correct. There can be an instance where for a specific orientation of the cube and the angle at which the light source incidences on the corner of the cube, the shadow will be cubic in nature. So, not always it is true that the light source will form rectangular shadow.
Hope it clears your doubt in this regard.
Regards