a*sin(π/2-A)+b*cos(π-B)=0a*cosA + b*(-cosB)=0cosA/cosB=b/a由正弦定理有：b/a=sinB/sinAcosA/cosB=sinB/sinAsinA*cosA=sinB*cosBsin2A=sin2B∵A∈(0,π),B∈(0,π)∴有：2A=2B或2A+2B=πA=B或A+B=π/2∴△ABC是...