About geometry Use a plane to cut a cube, the following figure: 1 circle 2 rectangle 3 equilateral triangle 4 trapezoid 5 right triangle Some of them can not be regarded as cross sections____ A1, B2, C3, D4

About geometry Use a plane to cut a cube, the following figure: 1 circle 2 rectangle 3 equilateral triangle 4 trapezoid 5 right triangle Some of them can not be regarded as cross sections____ A1, B2, C3, D4

B. 1 and 5 can't
Who says equilateral triangles don't work
Right triangles must not work. If you don't believe me, please give me a counterexample

A fan-shaped side unfolding is a semicircle. Find the ratio of the bottom area to the side area

A fan-shaped side is a semicircle. The fan-shaped itself is a plan. How can it be expanded? It's a cone, isn't it?
Just draw the picture. The hypotenuse of the cone is the radius of the unfolded semicircle. The circumference of the cone bottom is the circumference of the semicircle. To clarify these relations, I think there should be no problem in doing it. Think about it again and do it well

Mathematics problems of grade one in junior high school

(2) if the two angles are not equal, then the two angles are not opposite to the vertex angle () (3) two straight lines are cut by the third straight line, and the same angle is equal () (4) if the straight line ‖, then ‖ () (...)

As shown in the figure, △ ABC ≌ △ ade, ∠ B = 30 °, ∠ e = 20 ° and ∠ BAE = 105 °, calculate the degree of ∠ BAC=______ ．

∵ △ ABC ≌ △ ade & nbsp; and ∠ B ≠ e, ≠ C = ∠ e, ∠ B = ∠ D; and ≠ BAC = 180 ° - B - ∠ C = 180 ° - 30 ° - 20 ° = 130 °

Fill in the blanks with in, on, behind, in front of, under
The teacher is () the blackboard. 2, the blackboard is () the teacher. 3, the windows are () the wall. 4, the book is () the desk. 5. The bag is () the desk

in front of
behind
in
on
in/on/under
The last one depends on the specific situation,

Write a poem according to the content of the little match girl

In the world of cold wind, at the moment of new year's coming, in a corner of the city, the curled up body is shivering. One after another, the match is lit again and again. In the light of the fire, it seems that there are relatives calling again. The little girl smiles because she hears the call. After the last match is lit, her world becomes so perfect. In the smile, she sweetly falls asleep

The sum of a fraction and denominator is 53. If the denominator is added with 17, the fraction can be reduced to one sixth. What is the fraction?

10 out of 43

What are the five open syllable and closed syllable words?

1. Open syllable 1) a single syllable ending with a vowel
2) Syllables ending with consonants (except R) + silent E. example: make, like
*In stressed open syllables, vowels are pronounced by letter name
A syllable that ends with one or more consonants (except R) and has only one vowel in the middle,
They are called closed syllables
*Vowels are pronounced as short vowels in stressed closed syllables

Eight English books 48 pages 3A translation

As shown in the figure, in △ ABC, CD is the middle line on AB, and Da = DB = DC
1. Given ∠ a = 30 °, calculate the degree of ∠ ACB
2. Given ∠ a = 50 °, calculate the degree of ∠ ACB
3. Given ∠ a = x °, calculate the degree of ∠ ACB
4. Sum up a conclusion

⒈∠ACB=90°
⒉∠ACB=90°
⒊∠ACB=90°
4. If the center line on one side of a triangle is equal to half of this side, then the opposite angle is a right angle