cosα等于1/7,α等于arc cos1/7=81.786789298261811210965050519741)sin(α+β)等于5倍(根号3)/14 α+β=180-38.21321070173818878903494948026=141.78678929826181121096505051974β=60sin(α+β)等于5倍根号3/14属...