∫∠cod = 60, ∴δocd is an equilateral triangle,

∴CD=OC，

∵∠ cdf = 45, ∠ DCB = 90, CDF is an isosceles right triangle,

∴CD=CFOC,∠OCF=30，

∴∠cof= 1/2( 180-∠ocf)= 75 .