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
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