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1.B 2。 C 3。 D 4。 C 5。 C 6。 A seven. C 8。 A nine. A 10。 D 1 1。 A 12。 C

13. 14. 15. 16. 17. 18.

19.AB =, the equation of straight line AB is, that is,

Suppose there is a point C on the straight line x-3y+3=0, so that the area of triangle ABC is equal to 14, and the coordinate of C is, on the one hand, m-3n+3=0①, on the other hand, the distance from point C to straight line AB is, because the area of triangle ABC is equal to 14, then it is ② or ③. Get ① ② at the same time. Simultaneous ① ③ solution.

To sum up, there is a little C or on the straight line x-3y+3=0, which makes the area of triangle ABC equal to 14.

20.( 1) Similarly,

and

(2) Connect AC, BD intersects O, O is the midpoint of PD,

2 1. Proof: (1). Cube ABCD-a1b1c1d1,,,

(2) Take the midpoint of AB, followed by A 1P, which is simple and verifiable; ,

That is to say, the angle formed by AE and D 1F is

(3) take the midpoint q of CC 1, connect it with FQ, and do it again.

Say it again,

So FH is the distance from f to plane FQD 1A 1, and we can get:

So the distance from point f to plane A 1ED 1

22.( 1) comes from ∴. At this time, the equilibrium price is 300,000 yuan/ton and the equilibrium demand is 40 tons.

(2) If the new equilibrium price is 10000 yuan/ton, then from ∴, at this time =38, that is, the new equilibrium price is 320000 yuan/ton, and the equilibrium demand is 38 tons.

23. Solution: (1) A parallel line passing through a point on a plane is a straight line.

∵ ‖ , ‖ ,∴ ‖ .

Proof: (2) It is easy to prove ⊥ face, ∴⊥ face, and the same principle can prove ⊥ face,

Another =, ∴⊥ face.

Solution: (3) The distance from a straight line to a surface is the distance from a point to a surface, that is, the distance from a point to a surface.

The distance of the surface is recorded as, in the triangular pyramid.

That's ...

Solution: (4)

24. The linear equation of (1) crease is.

(2) If the coordinate of point a' is (a, 1), then the coordinate of point E of line segment aa' is (,), ∴aA'=, ∴ is an equation of a circumscribed circle with a radius of ∴.

.

When the circumscribed circle of is tangent to the straight line BC, the distance from point E to BC is equal to, and the distance from point E to BC is 2-, ∴ =2-.

The equation for finding a circle is.