This is a free lesson from our course in Trigonometry
In this lesson you'll learn more details of how to find the values of the sine and the cosine functions using the sum and difference formulas.
It is explained by instructor with the help of a video having some examples and
practice questions with solution. It is used in trigonometric applications to find the values of sine and
cosine functions for which the angle measures are given in degree or in radians and also to evaluate expressions for which the
angle measures of A and B are
unknown.
(More text below video...)
(Continued from above)
For example: Let us find value of sin (A + B);
where sin A = 3/5, cos B = 9/41 and 0 < A,
B<
/2.
You can use Pythagorean Theoremx^{2} + y^{2}
= r^{2} and sin A = 3/5 i.e. y/r,
to get cos A = 4/5.
Similarly, using the Pythagorean Theorem and cos B = 9/41 i.e. x/r,
you'll get sin B = 40/41. Now substitute these values in sin (A
+ B) = sin A cos B + cos A sin B.
You will get the answer 187/205.
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