kill(all)$

van=facebook.com/LearningCalculus$

xGivenL(L):=(2*sqrt((sqrt(2)-1)*sqrt(sqrt(2)+2)+3*sqrt(2-sqrt(2)))*sqrt(3)*abs(L))/
          ((2-sqrt(2))^(3/4)*(sqrt(2)-1)*sqrt(sqrt(2)+2)+(2-sqrt(2))^(1/4)*(sqrt(2)+2));

xGivenL(1);

float(%);