The denominator is x 2-5x+a.

When x=2, the denominator is -6+a, so when a=6, the denominator is meaningless.

When x 2-5x+a = 0, the discriminant △ = (-5) 2-4a = 25-4a,

∫a < 6，

∴△>0,

The equation x2-5x+a=0 has two unequal real roots.

In other words, x has two different values, which makes the score meaningless.