It s still geometry, hahaha, and there s a class

Because it is a straight triangular prism, the face a1b1c1 aa1 bb1 cc1 face abc.

So the bottom ACC1A1 is a square, then the bottom diagonal AC1 and A1C are bisected perpendicular to each other.

Let the intersection of AC1 and A1C be n, then N is the midpoint of AC1 and M is the midpoint of AB, so Mn BC1, so BC1 is A1MC

Connecting the bn, because it is a straight triangular prism, the face a1b1c1 aa1 bb1 cc1 surface abc

And because ac bc, the bc surface acc1a1, and ac=cc1, so ab=bc1

n is the midpoint of ac1, so bn ac1, so ac1 is a1bc

6), Straight lines perpendicular to each other then their slopes are reciprocal to each other, or their product = 1

Therefore, ax-y+b=0 is changed to y=ax+b, and the slope is a; x-3y+1=0 is changed to y=x 3+1 3, so a=3

5), P is true and Q is false, the choice can come by yourself.

4) If it is x+y-4<0 it is sufficient and unnecessary, if it is x+y+4<0 it is neither sufficient nor necessary.

The so-called sufficient means that the result can be obtained with certainty after the conditions are met.

And the so-called necessity means that after knowing the result, you can definitely get the conditions given.

For example, if x<0 and y<0, then it can be affirmed that x+y-4<0 is sufficient; And after knowing x+y-4<0, I can't get it.

There will be x<0, y<0.

，-3） ,0） 3.I always feel that both angles are changing, and the limit case n is parallel to CN and BM at the origin.

Because the surface area is reduced by 162 square centimeters, the cube side length is equal to 9 centimeters, and because the two cubes are combined into a cuboid, the length of the cuboid is equal to 18 centimeters, the width is equal to 9 centimeters, and the height is 9 centimeters. So the volume of the cuboid is 18x9x9 = 1458 cubic centimeters.

162 2=81 Since it is an edge x side 81 = 9x9, it means that the side length of the cube is 9cm volume = base x height x width 18x9x9 = 1458

The surface area is reduced by 162 square centimeters, and the side length of the cube is 9 cm, and the volume of the cuboid is: 18x9x9 = 1458

Because also because ab = de, the two triangles are congruent (corners).