Question

2) cos(60° + a) + cos(a – 60°)
Помогите пожалуйста ​

Answer 1

(cos60cos a+sin60sin a)-(cos60cos a- sin60sina)=0;

cos a-(cos60cos a+sin60sin a)-(cos60cos a- sin60sina)=0;cos a-cos60cos a-sin60sin a-cos60cos a+sin60sin a=0;

cos a-(cos60cos a+sin60sin a)-(cos60cos a- sin60sina)=0;cos a-cos60cos a-sin60sin a-cos60cos a+sin60sin a=0;cos a-2cos60cos a=0;

cos a-(cos60cos a+sin60sin a)-(cos60cos a- sin60sina)=0;cos a-cos60cos a-sin60sin a-cos60cos a+sin60sin a=0;cos a-2cos60cos a=0;cos a-2*1/2coos a=0