易知C＜π/2
cos2C=cos^2C-sin^2C=3/5
cos^2C+sin^2C=1
cosC=2√5/5 sinC=√5/5
,∠B=45º,b=√10,sinC=√5/5
由正弦定理得到c=2
sinA=sin(B+C)=sinBcosC+sinCcosB=3√10 / 10
三角形的面积=1/2*bc*sinA=3