"Leonardo had studied the use of math for commercial purposes at his abacus school, but from Verrocchio he learned something more profound: the beauty of geometry. After Cosimo de' Medici died, Verrocchio designed a marble-and-bronze slab for his tomb, which was finished in 1467, a year after Leonardo became his apprentice. Instead of religious imagery, the tomb slab featured geometrical patterns dominated by a circle inside a square, as Leonardo would use for his drawing Vitruvian Man. Inside the design, Verrocchio and his workshop carved carefully proportioned rectangles and half-circles in colors that were based on harmonic ratios and the Pythagorean musical scale.

There was harmony in proportions, Leonardo learned, and math was nature's brushstroke."