By failing to prepare, you are preparing to fail.
H2017-04-02T20:06:04+10:00

## H

##### Definition
half life the time it takes for a substance to decay to half its original weight
happy number a positive integer whose digits, when squared, add to 1
23 ==> 22 + 32 = 4 + 9 = 13 ==> 12 + 32 = 1 + 9 = 10 ==> 12 + 02 = 1  ∴ 23 is a happy number
44 ==> 42 + 42 = 16 + 16 = 32 ==> 32 + 22= 9 + 4 ==> 13 ==> 12 + 32 = 1 + 9 = 10 ==> 12 + 02 = 1  ∴ 44 is a happy number
391 ==> 32 + 92 + 12 = 9 + 81 + 1 = 91 ==> 92 + 12 = 82 ==> 82 + 22 = 64 + 4 = 68 ==> 62 + 82 = 36 + 64 = 100 ==> = 12 + 02 + 02 = 1  ∴ 391 is a happy number
HCF Highest Common Factor, the highest number that fits evenly into two or more numbers
heptagon a polygon with 7 sides
Heron’s formula used to find the area of a triangle when three sides are known. $A=\sqrt{s(s-a)(s-b)(s-c)}$, where $s=\frac{a+b+c}{2}$ S is also known as the semi-perimeter of the triangle
hexagon a polygon with 6 sides
hexahedron a solid with six faces. A regular hexahedron is a cube – all six faces the same.
horizontal a flat line or plane that runs parallel to the horizon

horizontal line test when a horizontal line is drawn through a function if that line only intersects with the function once, it is a one-to-one function and will have a naturally occurring inverse function
hyperbola the most basic hyperbola is the function $y=\frac{1}{x}$
hypotenuse the longest side of a right triangle, opposite the right angle