ω: the coefficient representing the angle x of a variable in trigonometric function, such as y = sin(ωx+ψ), t = 2π/|ω|.

∏: In algebra, it is a quadrature symbol. ∑: In algebra, it is the symbol of summation. (Please compare and understand)

π:π。 Solid geometry represents a plane.

λ: Represents a constant in algebra. In analytic geometry, it is expressed by constant ratio coefficient or undetermined coefficient.

ψ, ψ: Angle, auxiliary angle.

ε: A small enough positive number in the definition of calculus limit.

η: Same as λ.

φ, φ: Angle, auxiliary angle.