If x = 1 + $$\surd{2}$$+ $$\surd{3}$$, then the value of 2x^{4}- 8x^{3}- 5x^{2} + 26x - 28 is

x = 1 + $$\surd{2}$$+ $$\surd{3}$$

=> $$ (x-1)^2 = ( \surd{2}+ \surd{3})^{2} $$

=> $$ x^2 + 1 -2x = 5 + 2\surd{6} $$

=> $$ x^2-2x =4 + 2\surd{6} $$ ----------- (1)

Squaring on both sides

=> $$ (x^2-2x)^2 = x^4 + 4x^2 - 4x^3 = 40 + 16\surd{6}  $$ ------ (2)

Now, 

$$2x^{4}- 8x^{3}- 5x^{2} + 26x - 28 = 2(x^{4}-4x^{3})- 5x^{2} + 26x - 28 $$ ---- (3)

Substituting values in (1) & (2) in equation (3), we get value as $$ 6 \surd {6} $$