sin(A+B) = sinA*cosB + cosAsinB cosA*sinB = sin(A+B) - sinA*cosB = sin(A+B) - 1/2 因为 1≥sin(A+B)≥ -1 所以 1/2 ≥ cosAsinB ≥ -3/2 sin(A-B) = sinA*cosB - cosAsinB cosA*sinB = sinA*cosB - sin(A-B) = ...