在ΔABC中,若b2=ac,则cos(A—C)+cosB+cos2B的值是_____.
1。解析:b2=ac,sin2B=sinAsinC,cos(A--C)+cosB+cos2B=cosAcosC+sinAsinC+cosB+1—2sin2B=cosAcosC+sinAsinC+cosB+1—2sinAsinC=cosAcosC—sinAsinC+cosB+1=cos(A+C)+cosB+1=1.
在ΔABC中,若b2=ac,则cos(A—C)+cosB+cos2B的值是_____.
1。解析:b2=ac,sin2B=sinAsinC,cos(A--C)+cosB+cos2B=cosAcosC+sinAsinC+cosB+1—2sin2B=cosAcosC+sinAsinC+cosB+1—2sinAsinC=cosAcosC—sinAsinC+cosB+1=cos(A+C)+cosB+1=1.