Quadruple Angle Formulas/Hyperbolic Cosine

Theorem

 * $\cosh 4 x = 8 \cosh^4 x - 8 \cosh^2 x + 1$

where $\cosh$ denotes hyperbolic cosine.

Also see

 * Quadruple Angle Formula for Hyperbolic Sine
 * Quadruple Angle Formula for Hyperbolic Tangent