Close-up of a crumpled, slightly yellowed draft paper filled with handwritten mathematical problem-solving process, featuring complex formulas, derivation steps, and geometric diagrams in black pen or pencil. Show thought trajectory with arrows, brackets, and annotations, including erasure marks and calculation sketches. Coffee stains and edge wear, soft natural lighting, realistic texture of paper and ink strokes, detailed focus on academic study atmosphere, photorealistic style, high detail.