请数学高手帮忙！！！

1.8^x + 8^(-x) = 2^3x + 2^(-3x)
[2^x+2(-x)]^2=2^2x + 2^(-2x) + 2 = a^2
2^2x + 2^(-2x) = a^2-2
[2^2x + 2^(-2x)]*(2^x+2^(-x)) = 8^x+8(-x) + 2^x+2^(-x) = a(a^2-2)
所以 8^x+8(-x) = a(a^2-2) - a
2. x+y=12 xy=9 x （x^1/2-y^1/2）/（x^1/2+y^1/2）
=(x^1/2-y^1/2)^2/锋岩（x^1/2+y^1/2）* (x^1/2-y^1/银神御2)
=(x+y-2(xy)^1/2)/(x-y)
(x-y)^2 = (x+y)^2 - 4xy , x-y < 0
剩下的代入就好瞎卖了

1.立方和公式：森告宴a^3+b^3=(a+b)*(a^2-ab+^b^2)
8^x+8^(-x)=(2^x)^3+[2^(-x)]^3=[2^x+2^(-x)]*(a^2-2+1)=a*(a^2-1)

2.（x^1/2-y^1/此银2）/（x^1/2+y^1/2）=(x-y)/（x+y+2根号xy）=（根友慎号3）/3

8^x+8^(-x)=a^3-3*a;
-sqrt(3)/3