(1) 2cos(5π/3)*cos(π/3-A)-cos(A)=0.5
2cos(2π-π/3)*cos(π/3-A)-cos(A)=0.5
2cos(π/3)[cos(π/3)cos(A)+sins(π/3)sin(A)]-cos(A)=0.5
1/2*cos(A)+√3/2sin(A)-cos(A)=0.5
√3/2sin(A)-1/2cos(A)=0.5
sin(A-π/6)=1/2
A-π/6=π/6 或 A-π/6=5π/6
A=π/3 或 A=π (舍去）
即A=60º
(2)题目有错.