There is a little bit of controversy in mathematics and a controversial question in mathematics

A dichotomy is used to find faults. Check the middle first, if there is a problem, then the second half is normal, the first half is a problem, if there is no problem, it means that the first half is normal, and the second half is a problem. In the same way, then check the pole in the middle of the problematic part, and in the same way, if there is a problem, continue to search in this part using the dichotomy method.

9 times. There are 399 sections of wire between two poles.

So 9 times.

20 kilometers apart, the distance between the two adjacent poles is 50 meters, 400 sections of wires, 401 poles, odd number of poles to climb ** (if it is 400, then there are two in **, it is not easy to choose).

1 = 200 remaining unknown, 2 = 100 remaining unknown, 3 = 50 remaining unknown, 4 = 25 remaining unknown, 5 = 13 remaining unknown (cannot be divided equally, only the longer one can be assumed), 6 = 7 remaining unknown, 7 = remaining 4 unknown, 8 = 2 remaining unknown, 9 can be determined.

Refer to binary method encoding, 20,000 50=4000;

12 + 1 = 13 times.

The topic is a little different, but the method is the same.

9 times. There are 399 sections of wire between two poles.

So 9 times.

Let the equation be x 2 + ax + b = 0

A did not misread the coefficient of the term once, according to Veda's theorem, a=-(x1+x2)=-5 B did not misread the constant term, according to Vedder's theorem b=x1*x2=-24x 2-5x-24=0

x-8)(x+3)=0

x1=8,x2=-3.

The last +3 of the first step is ** coming? So answer 0 is wrong :

Original A BC B AC C AB 3 ??

It should be: original = a bc b ac c ab +3 -3= (a b c 3abc) abc -3 [a b) c 3a b 3ab 3abc] abc -3

[（a＋b＋c）（a²＋b²＋2ab－ac－bc＋c²－3ab（a＋b＋c）]/abc -3

（a＋b＋c）（a²＋b²＋2ab－ac－bc＋c²－3ab）/abc -3

The first is right.

The second one is wrong.

a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)=－a²/bc－b²/ac－c²/ab＋3

There shouldn't be a 3 behind this.

You just need to get this step right, and then you'll get the next two answers the same.

The answer is -3

Since a+b+c=0, then a, b, and c are not 0, and the sum of any two of them is not 0

That is to say, LAL, LBL, LCL are not equal.

I don't think the second solution is right, because for no reason I add a three-square: a, bc, b, c, ab, 3

This piece should not add three, and you try to take the general points in parentheses in the original formula and then bring in a b c, a c b, b c a to get the original a bc b ac c ab

Where did the 3 come from??

Propose that abc is equal to (a+b+c) (1 b+1 c+1 c+1 a+1 a+1 b) because (a+b+c) is equal to 0, so the original formula is 0, because the premise abc is the denominator, so abc is not 0, the first method does not take this into account, resulting in the generation of root addition. Thank you.

How did a +3 come out of the second method?,There shouldn't be.。

Because the question is about the minimum amount to plant, the worst-case scenario needs to be taken into account, which is that the survival rate is 75%.

Then at least it is needed.

1200 75% = 1600 trees.

That is, at least 1,600 trees should be planted to ensure that 1,200 trees will survive.

Hope it works.

x*80%>=1200

x>=1200/80%=1500

So plant at least 1,500 trees.

At least, then the most optimistic scenario is to be calculated, that is, a higher survival rate.

To seek the most, it is necessary to take a lower survival rate according to the pessimistic situation.

Plant 1,500 trees, and if the survival rate is 80 percent, 1,200 trees will survive.

In other words, it is possible to plant 1,500 trees.

So at least of course the least 1500 trees to choose.

At least a few should be planted, and a high survival rate should be considered, so it is 1200 80% = 1500

What you want to consider is the lowest survival rate, which is actually 1200 divided by 75%.

At least 1600, if 1500, the survival rate is only, only 1125 classes survive, not met.

ay1=cos2x1=sin(π/2-2x1)y2=sin(π/6-2x2)

Let 2-2x1= 6-2x2

4-x1=π/12-x2

x1=x2+π/6

Therefore, it is necessary to translate the function y=sin( 6-2x) to the right by 6 units of length.

The correct answer is A

Because y=sin[ 6-2(x- 6)]=sin( 2-2x)=cos2x

So by translating the function y=sin( 6-2x) to the right by 6 units of length we get y=cos2x

y=sin(π/6-2x)=cos(π/2-(π/6-2x))=cos(2x+π/3)

cos(2x+3) is 3 to the left of cos2x, so you need to move 3 to the right. Choose C.

cy=sin(π/6-2x)=sin2(π/12-x)

Translate 3 units to the right.

Then the above equation = sin2 ( 12-x- 3) = sin2 (- 4-x) = sin(- 2-2x) = cos(-2x) = cos2x

y=sin( 6-2x)=cos(2x- 3) to get y=cos2x just need to pan 3 to the right

So choose C

(17+3)*2=40.

40+2)*2=84.

A: There are 84 eggs in total. (Use the reverse deduction method to solve the problem).

To verify: 84 2-2 = 40.

40 2-3 = 17 pcs.

(17+3)*2=40.

40+2)*2=84.

A: There are 84 eggs in total.

Boys donate two-thirds of girls' contributions.

The number of donations for girls is 1 (1+2 3) = 3 5 for the number of donations from the class

160 (3 5-2 5) = 800 RMB.

Solution: Set up this class to donate a total of X yuan to the disaster area.

2/3*(40%x+160)=x-(40%x+160)4x/15+320/3=

x/3=800/3

x=800A: This class donated a total of 800 yuan to the disaster area.

From the size in the figure, it can be seen that the bottom surface of a regular triangular prism is an equilateral triangle with a side length of 2, and the height of the piece that is cut off is not given, assuming that it is 1

Then, the side view should be a right-angled trapezoid, with a base edge length of 2 (the height of the triangular prism) and a base edge length of 1 (the remaining height after the triangular pyramid is chipped), and the height of the reminder is the height of the equilateral triangle No. 3

So the area is (3*root3) 2

From the top view and the front view, it can be seen that the picture is a regular Mitsubishi cone, the upper and lower surface is a regular triangle with a side length of 2, and the side height is 2

So the side view is a rectangle with a length of 2 and a width of 3.

That is, the area of the side view is 2 3

It is equivalent to a triangular prism with a corner obliquely cut off on it, and the side should be a trapezoid, s=1 2(2- 3+2)*1=(4- 2) 2

The triangular prism should be a square on the side, 2 in width and 2 in height, and 4 in area

It should be like this, find the area of the side as three-twoths of the root three...

Friends should be straight triangular prisms, imagine that.

The distance between places A and B 2 is: kilometers and kilometers.

After 2 hours the speed is 87 km/h. Therefore, the distance between A and B is 87*

The car has traveled 85+174 km.

So 87* remains