根据和差化积公式：sinx+siny=2sin[(x+y)/2]cos[(x-y)/2]= log7 2cosx+cosy=2cos[(x+y)/2]cos[(x-y)/2]= log7 4两式相除,得：sin[(x+y)/2] / cos[(x+y)/2]=1/2即：tan[(x+y)/2]=1/2∵有1+(tanα)^2=(secα)^2 且 cos...