X1^2 - X2^2 = 8
(X1 + X2)(X1 - X2) = 8
根据韦达定理有:X1 + X2 = 4
所以 4(X1 - X2) = 8
则 X1 - X2 = 2
而 (X1 - X2)^2 = (X1 + X2)^2 - 4X1X2 = 4^2 - 24K = 16 - 24K
那么 16 - 24K = (X1 - X2)^2 = 2^2 = 4
所以 K = 1/2