[Index]
Introduction Essence Memorizing Basic
Formulas
Sum and Difference Formulas
Double & Triple Angle
Formulas
Half Angle Formulas
Product to Sum Formulas
Sum to Product Formulas
All Formulas
Understanding Summarizing Examples Exercises Final
thoughts
 |
Half-Angle Formulas:
Formulas 1, 2 and 3 are all
fractions of cosine functions.
Note the order of 1 and cosine:
is behind 1. The sine
squared and tangent squared have
negative signs while cosine
squared has a positive sign in the numerators. Only tangent squared has the denominator of 
, the rest have a denominator of 2.
Formulas 4, 5 and 6, these are the
same as the squared formulas except everything is square-rooted and
also don't forget the "+" and "-" signs, which depend on the
functions of 
and which
quadrant is in. For
example, if is in second
quadrant, then 
has positive
sign and 
, 
have negative signs. Here is a way to remember,
put one of the four words in "All
Students Try Cheating" in
the order of quadrant I, II, III, IV. And the first letter of each
word represents the first letter of I. All positive, II. Sine positive, III. Tangent, IV. Cosine.
