sin27cos33+cos57sin63
=sin27cos33+cos27sin33
=sin(27+33)
=sin60
=√3/2
cosA=-1/2,sinA=√3/2
cosB=√2/2 sinA=√2/2
sinC=sin(A+B)=(√3/2)(√2/2)+(-1/2)(√2/2)=(1/4)(√6-√2)
三角形中不可能有2个钝角
cosA0 cosA>0,cosB
sin27cos33+cos57sin63
=sin27cos33+cos27sin33
=sin(27+33)
=sin60
=√3/2
cosA=-1/2,sinA=√3/2
cosB=√2/2 sinA=√2/2
sinC=sin(A+B)=(√3/2)(√2/2)+(-1/2)(√2/2)=(1/4)(√6-√2)
三角形中不可能有2个钝角
cosA0 cosA>0,cosB