72/73(a2-b)-78/79(2a+10b)-1/4(a+b)
=72/73((-0.2)^2-0.04)-78/79(2*(-0.2)+10*0.04)-1/4(-0.2+0.04)
=72/73(0.04-0.04)-78/79(-0.4+0.4)-1/4(-0.16)
=72/73*0-78/79*0+0.04
=0.04