SinA=4sinBcosC because sinA=2sinBcosC and cosC= 1/4 because sinA=sinB, cosC= 1/2 or cosC=- 1/2 when cosC= 1/2 and C = 60 because SINA = At this point, the triangle ABC is an equilateral triangle. When cosC=- 1/2, C = 120, SINA = SINB.