\(a,\left(a-b\right)-\left(b+c\right)+\left(c-a\right)-\left(a-b-c\right)=-\left(a+b-c\right)\)

\(VT=a-b-b-c+c-a-a+b+c=-a-b+c=-\left(a+b-c\right)=VP\)

\(b,\left(2x-y\right)-\left(x+y\right)=x-2y\)

\(VT=2x-y-x-y=x-2y=VP\)

\(a,3\sqrt{27}-2\sqrt{75}+3\sqrt{12}-2\sqrt{147}\)

\(=9\sqrt{3}-10\sqrt{3}+6\sqrt{3}-14\sqrt{3}=-9\sqrt{3}\)

\(b,2\sqrt{2}+\sqrt{32}-\dfrac{1}{3}\sqrt{450}+\dfrac{2}{7}\sqrt{392}\)

\(=2\sqrt{2}+4\sqrt{2}-5\sqrt{2}+4\sqrt{2}=5\sqrt{2}\)

\(c,\sqrt{\left(2+7\right)^2}+\sqrt{\left(10-\sqrt{7}\right)^2}\)

\(=\sqrt{81}+\left|10-\sqrt{7}\right|=9+10-\sqrt{7}=19-\sqrt{7}\)