1、(1/3)*[3a*根号(3a)] - a*a*根号(3a)/a + 3a*根号(3a)/3 - (4/3)*6a*根号(3a) = -7a*根号(3a)
2、(a + 1/a)^2 = a^2 + 2 + 1/a^2 = (a - 1/a)^2 + 4 = 6;所以a+1/a为±根号6
3、x^2 + 2xy + y^2 = (x + y)^2 = (根号2 + 1 + 根号2 - 1)^2 = 8
4、xy = (2 - 根号3)*(2 + 根号3) = 4 - 3 = 1;x^2 + y^2 = (x + y)^2 - 2xy = 4^2 - 2 = 14
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