Question

△ABV中,A为锐角,若向量m=(cosA,sinA),向量n=(cosB,sinB),向量m·向量n=√3sinB-c

Answer 1

1)向量m·向量n=cosAcosB+sinAsinB=√3sinB-cosC

cosC=-cos(A+B)

cosAcosB+sinAsinB=√3sinB+cos(A+B) cos(A+B)=cosAcosB-sinAsinB

cosAcosB+sinAsinB=√3sinB+cosAcosB-sinAsinB

sinA==√3/2 A=π/3

2)sinA=cosBsinC =cosBsin(A+B) =√3/2 你再化化吧 我晕了

s圆=πR²=4π R=2

a/sinA=2R=4 a=2√3