A=4a^2b-5b^2B=-3a^2b+2b^2A+B=4a^2b-5b^2-3a^2b+2b^2=a^2b-3b^2C=-(A+B)=3b^2-a^2b=3*(1/2)^2-(-1/2)^2*(1/2)=3/4-1/8=5/8
