sinAcosC+sinCcosA-2sinBcosB=0
sin(A+C)-sin(2B)=0
sin(180°-B)-sin(2B)=0
sinB=sin(2B)
∵B≠2B
∴B=180°-2B
B=60°
A=π/6=30°
C=180°-60°-30°=90°
2SIN^2A+COS(A-C)
=2*(1/2)^2-1/2
=0