9c^2-4b^2/18c^2-12bc при b=0,5, с=2/3

9c^2-4b^2/6c(3c-2b)=9*(2/3)^2-4*(0,5)^2/6*2/3(3*2/3-2*0,5)=4-1/4(2-1)=3/4