a) $2.\sqrt{6}.(-\sqrt{6})=-2.\sqrt{6}.\sqrt{6}=-2.(\sqrt{6}){2}=-2.6 = -12$
b) $\sqrt{1,44}-2.(\sqrt{0,6})^{2}=1,2 -2.0,6 = 1,2 - 1,2 = 0$
c) $0,1.(\sqrt{7})^{2}+\sqrt{1,69}=0,1.7+1,3=0,7+1,3=2$
d) $(-0,1).(\sqrt{120})^{2}-\frac{1}{4}.(\sqrt{20})^{2}=(-0,1).120-\frac{1}{4}.20=-12 - 5 = -(12+5)=-17$