The proposition a 0 is what condition of the proposition x ay 1 0 parallel y axis .

It is a sufficient condition.

Analysis: From a=0, see if the straight line ax-y+1=0 and the straight line x-ay-1=0 can be verticalized, and vice versa, see if the straight line ax-y+1=0 and the straight line x-ay-1=0 can be vertically to get a=0

Comments: This question examines the judgment of necessary conditions, sufficient conditions and sufficient conditions, and the methods for judging sufficient and necessary conditions are:

If p q is a true proposition and q p is false, then the proposition p is a sufficient and unnecessary condition of proposition q;

If p q is a false proposition and q p is a true proposition, then the proposition p is a necessary and insufficient condition of proposition q;

If p q is a true proposition and q p is a true proposition, then the proposition p is a sufficient and necessary condition of the proposition q;

If p q is a false proposition and q p is false, then the proposition p is a proposition q, i.e., it is not sufficient or necessary

Judge the scope of proposition P and proposition Q, and then judge the relationship between proposition P and proposition Q according to the principle of "who is greater and who is necessary, who is small and who is sufficient".

The key to solving this problem is that the straight line a1x+b1y+c1=0 is vertically equivalent to a1a2+b1b2=0 and a1a2+b1b2=0

a=0, to be able to push out x=1 parallel y-axis, here is a sufficient condition.

x-ay-1=0 should be parallel to the y-axis, either a=0, or y=0Because y is not equal to 0.

So only a=0 can be pushed

This proposition is a sufficient condition.

This should be a matter of envy and defeat.

than brother elimination, such as a=(1,0; 0,0),x =(1;2),y=(1;3)ax=ay=(1;0), but x and y are not equal.

represents the replacement of dry round rows).

The straight line x+2ay-1=0 is parallel to (a-1)x-ay+1=0, so 1*(-a)-2a*(a-1)=0

So a=0 or a=1 2

When a=0, both straight lines are x=1, which coincides and is rounded.

So a=1 2

a=-1, the two lines are x-y-1=0, x-y-3=0, and the two lines are parallel.

If two straight lines are parallel, then -a=-1 a(a≠0), 1≠(1 2a) a, and a= 1 (a=1 rounded).

Therefore, p is a sufficient and necessary condition for q to be established, i.e., a sufficient and necessary condition.

(1) Parallel requires the same slope (a-1) 2 = 1 a (a-2)(a+1)=0 a= 2

or -1 can be (2) When perpendicular, the slope requirement is multiplied by -1 to obtain a= 1 3

(1) Parallel: (a-1) 1=-2 -a simplification yields a 2-a-2=0 solution yields a=2 or -1.

2) Vertical: [(a-1) 2]*(1 a)=-1 simplification yields a=1 3

Sufficient but not essential.

Because 1 a = a 1 i.e. a 2 = 1 a = 1 or a = -1

When x is less than 0, the inequality does not hold, so a is incorrect;

a= 1 is two straight lines perpendicular to the essential strip, so b is incorrect;

The sufficient and necessary condition for straight lines A and B to be straight lines on different planes is that the two straight lines are neither parallel nor intersecting, so C is incorrect, and D is known to be correct according to the negative form of the special proposition Collapse Laohong, so D is chosen