已知sin(x+20度)=cos(x+10度)+cos(x
题设条件可化为 sinxcos20+cosxsin20=2cosxcos10 →sinxcos20=cosx(2cos10-sin20) →tanx=(2cos10-sin20)/cos20 =[2cos(30-20)-sin20]/cos20 =(2cos30cos20+2sin30sin20)/cos20 =(2cos30cos20)/cos20 =2cos30 =根3. 注:以上省略了“度”