.
1. First calculate = .
2. Then calculate = .
3. Then apply trigonometry formulas
sin(a + b) = sin(a)*cos(b) + cos(a)*sin(b)
sin(a - b) = sin(a)*cos(b) - cos(a)*sin(b)
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If you want to see many other similar solved problems, look into the lessons
- Calculating trigonometric functions of angles
- Advanced problems on calculating trigonometric functions of angles
- Evaluating trigonometric expressions
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
- ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Trigonometry: Solved problems".
Save the link to this textbook together with its description
Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson
into your archive and use when it is needed.