H

**half plane: the set of all points in a plane that
lie on one side of a line in the plane.**

**harmonic sequence: a sequence is a harmonic sequence
if the reciprocals of the numbers
in the
sequence form an arithmetic sequence.**

**heptagon: a polygon with seven sides.**

**Heron's formula: a formula for the area of a triangle:
_________________
A
= (**

**where a, b, and c are the lengths of the sides of the
triangle, and**

*s* is half the perimeter.

**hexadecimal number: a number written in base sixteen.**

**hexagon: a polygon with six sides.**

**hexahedron: a polyhedron with six faces. A
regular hexahedron is a cube.**

**hyperbola: the set of all points in a plane such
that the difference of the distances to two**

**fixed points is a constant. The general equation
for a hyperbola is**

__x__^{2} - __y__^{2 }=
1

a^{2 }b^{2}

**hyperbolic functions: the hyperbolic functions are
defined as follows:**

**hyperbolic cosine: cosh x = (1/2)(e^{x}
+ e^{-x})**

**hyperbolic sine: sinh x
= (1/2)(e^{x} - e^{-x})**

**hyperbolic tangent: tanh x = sinh
x **

-------

cosh x

**hypotenuse: the longest side of a right triangle. The
side opposite the right angle in a
right triangle.**

**hypothesis: a proposition that is being investigated,
it has yet to be proven.**