This is a free lesson from our course in Trigonometry
This lesson walks you through how to use double and half angle formulas. It has
been explained by the instructor using video and with the help of some examples,
practice questions with solution.
Double and Half-Angle formulas are very useful in trigonometric applications e.g. rational functions of sine and cosine will be very hard to integrate without these
formulas. Similarly it would be useful to reduce the degree of difficulty, where
functions involving powers of sine and cosine are hard to integrate. Also the Double-Angle formulas may be used to generate easily the
Half-Angle formulas.
(More text below video...)
(Continued from above)
You'll learn the steps now; how to find out the value of
sin 2
and sin 2, if the value
of cos
is known and similarly to find the value of sin
/2 and cos
/2, if the value of
cos
is known. For example, cos 15
can be evaluated using the formula
cos (A/2) =
(1
+ cos A)/2.
cos (30/2)
=
(1 + cos 30)/2,
Substituting cos 30
=
3/2, you'll get
the answer
{(2 +
3)}/2.
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and sin 2
can be evaluated using the formula
(1
+ cos A)/2.