令 x=sin α,y=cos α,则x +y =√2 /2,①x^2 +y^2 =1,②x,y 属于[-1,1].①^2 -② 得2xy = -1/2.即 xy = -1/4,③ 由 ①②③ 得(1) (sin α)^3 + (cos α)^3 = x^3 +y^3= (x +y) (x^2 +y^2 -xy)= √2 /2 *(1 +1/4)= 5...