1) а)sin(П/5 + 3П/10)= sin(2П+3П/10) = sin(П/2)=1
б)cos(-30)=-√3/2
3)2cos (a+b)+(a-b)/2 • cos (a+b)-(a-b)/2 = ...
2cos 2a/2 • cos 2b/2 = ...
2cosa•cosb=2cosa•cosb
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Answers & Comments
1) а)sin(П/5 + 3П/10)= sin(2П+3П/10) = sin(П/2)=1
б)cos(-30)=-√3/2
3)2cos (a+b)+(a-b)/2 • cos (a+b)-(a-b)/2 = ...
2cos 2a/2 • cos 2b/2 = ...
2cosa•cosb=2cosa•cosb