Greek letters fill in where Roman letters run out — common in maths, physics and statistics.
Quick check
Which Greek letter is the standard symbol for a summation?
Letters you'll meet constantly
- π ≈ 3.14159 — circles, and far beyond.
- θ, φ — angles, especially in trig and polar/spherical coordinates.
- Σ — sum; Π — product.
- Δ — a change in something (Δx = change in x); lowercase δ — a tiny change.
- λ — wavelength, eigenvalues, rates; μ — mean, micro-, friction; σ — standard deviation; ρ — density, correlation.
Case matters: lowercase σ is a standard deviation, capital Σ is a sum. Lowercase δ is a small change, capital Δ is a (possibly large) change.
Most-used
- α, β, γ — angles, parameters
- θ, φ — angles in trig
- π — 3.14159…
- Σ — sum
- Δ, δ — change, small change
- ∞ (infinity), ∇ (nabla, vector calc)