Term

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 ==> 2^{2} + 3^{2} = 4 + 9 = 13 ==> 1^{2} + 3^{2} = 1 + 9 = 10 ==> 1^{2} + 0^{2} = 1 ∴ 23 is a happy number
44 ==> 4^{2 }+ 4^{2} = 16 + 16 = 32 ==> 3^{2} + 2^{2}= 9 + 4 ==> 13 ==> 1^{2} + 3^{2} = 1 + 9 = 10 ==> 1^{2} + 0^{2} = 1 ∴ 44 is a happy number
391 ==> 3^{2} + 9^{2} + 1^{2} = 9 + 81 + 1 = 91 ==> 9^{2} + 1^{2} = 82 ==> 8^{2} + 2^{2} = 64 + 4 = 68 ==> 6^{2} + 8^{2} = 36 + 64 = 100 ==> = 1^{2} + 0^{2} + 0^{2} = 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. $$A=\sqrt{s(sa)(sb)(sc)}$$, where $$s=\frac{a+b+c}{2}$$ S is also known as the semiperimeter 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 onetoone 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 