a)
S=\frac{2}{3}x^4+2x-1 ,
T=\sqrt{2\frac{7}{9}}x^4+x^2-3x=\sqrt{\frac{25}{9}}x^4+x^2-3x=\frac{5}{3}x^4+x^2-3x
S+T=\frac{2}{3}x^4+2x-1+\frac{5}{3}x^4+x^2-3x=
=\frac{7}{3}x^4+x^2-x-1
-------
=\frac{7}{3}\cdot 2^4+2^2-2-1=
=\frac{7}{3}\cdot 16+1=\frac{112}{3}+1=38\frac{1}{3}
b)
S=\frac{2}{\sqrt3}x^3-x^2+2=\frac{2\sqrt3}{3}x^3-x^2+2
T=-\sqrt3x^3+3x^2-1
S+T=\frac{2\sqrt3}{3}x^3-x^2+2+(-\sqrt3x^3)+3x^2-1=
=\frac{2\sqrt3}{3}x^3-\sqrt3x^3+2x^2+1=
=x^3(\frac{2\sqrt3}{3}-\frac{3\sqrt3}{3})+2x^2+1=
=-\frac{\sqrt3}{3}x^3+2x^2+1
-------
=-\frac{\sqrt3}{3}\cdot 2^3+2\cdot 2^2+1=9-\frac{8\sqrt3}{3}