Parallelogram (14 21:0:56) In ⊿ ABC, ∠ ACB = 90 degrees, D.E BC.AB (1) is quadrilateral ACEF a parallelogram? Why? (2) when ⊿ ABC satisfies what conditions, AE and FC are bisected vertically, and explain your conclusion. (3) can quadrilateral ACEF be a square? Why?

F is on the extension line of de. 1) quadrilateral ACEF is a parallelogram because AF ∥ CE angle DEB = angle AEF = angle cab AC ∥ ef2) when AE and FC are perpendicular to each other, quadrilateral ACEF is a diamond, AC = CE angle cab = 60 degrees, so when ⊿ ABC satisfies AB = 2Ac, it satisfies the meaning. 3) when quadrilateral ACEF is a square, point e falls at point D

How can a spacecraft land on the moon

Unlike the earth, the moon can use a parachute slowly. It is in a vacuum state. Therefore, when the lunar exploration spacecraft lands on the moon, it will start the landing engine and must use a rocket to recoil and land on the surface of the moon smoothly. To achieve a soft landing, it can't hit the moon hard

2 / 3x plus 1 / 2x equals 42. Unknowns

The distance from a to B is 180 km, and a car goes from a to B at an average speed of 70 km per hour. The function expression of the distance s km and the travel time t is

s=180-70t

If x = 5 is equation (2x-7) / 4 + (x-m) = (3x + 2) / 12

Substitute x = 5 into equation (2 * 5-7) / 4 + (5-m) = (3 * 5 + 2) / 12
3/9-m=17/12
m=117/17

It took two hours for a car to travel from place a to place B. in the first hour, it took three seventh of the whole journey, and in the second hour, it took 80 thousand

112 km
80/(1-3/7)=112

If a set a = {1,2} and B satisfies a ∪ B = {1,2}, then B has______ One

∫ set a = {1,2} has two elements. If a ∪ B = {1,2}, then B ⊆ a has 22 = 4 sets which satisfy the condition, so the answer is: 4

Factorization (x ^ 2 + 2x) (x ^ 2 + 2x-2) - 5

（x²+2x)(x²+2x-2)-5=(x²+2x)[x²+2x)-2]-5=(x²+2x)²-2（x²+2x)-5=(x²+2x)²-2（x²+2x)+1-6=(x²+2x-1)²-(√6)²=(x²+2x-1+√6)(x²+2x-1-...

There are 80kg apples in the fruit shop. The kilogram of oranges is 4 / 5 of that of apples. The kilogram of bananas is 3 / 4 of that of oranges. How many fruits are there in the fruit shop
There are 80kg apples in the fruit shop. The kilogram of orange is 4 / 5 of that of apple, and the kilogram of banana is 3 / 4 of that of orange?

A total of 80 + 80 × 4 / 5 + 80 × 4 / 5 × 3 / 4
=80+64+48
=192 kg

If the sum of the monomials 2xym-1 and - x2n-3y3 are still monomials, then the value of M + n is______ ．

∵ the sum of the binomial 2xym-1 and - x2n-3y3 is still a monomial, ∵ the binomial 2xym-1 and - x2n-3y3 are the same kind, ∵ 2n-3 = 1, M-1 = 3, ∵ M = 4, n = 2, ∵ m + n = 6

Parallelogram (14 21:0:56) In ⊿ ABC, ∠ ACB = 90 degrees, D.E BC.AB (1) is quadrilateral ACEF a parallelogram? Why? (2) when ⊿ ABC satisfies what conditions, AE and FC are bisected vertically, and explain your conclusion. (3) can quadrilateral ACEF be a square? Why?