Solid geometry, which focuses on the properties and relationships of three-dimensional objects, is less commonly taught today due to the rising emphasis on calculus and probability in mathematics education. Many concepts from solid geometry have been integrated into calculus, diminishing its standalone importance. Resources for learning solid geometry include various books and online materials, though specific recommendations were not provided in the discussion. The decline in its teaching reflects broader educational trends prioritizing other mathematical disciplines. Overall, solid geometry remains a valuable area of study, despite its reduced presence in curricula.