What a math problem!! Geniuses come to see 5

AOB = AOC + BOC = 2 BOC + BOC = 3 BOC = 36 * 3 = 108 degrees OD is the angular bisector of the angle AOB AOD=1 2 AOB=1 2*108=54 degrees AOC=2 BOC=2*36=72 degrees COD= AOC- AOD=72-54=18 degrees.

sinb sinc=b c= 2 2 where b = ac, c = ab

Let b = 2, c = 2 then ad=1 ac= 2, a=105°

CD=( 2- 6) 2 is obtained from the cosine theorem, and then ACD from the cosine theorem.

After A pours it to B, the ratio of the oil in bucket A to the oil in barrel B is 1:3, that is, A is 1 3 of B, and B pours 1 3 to A, then B has 2 3 left

And A also has 1 3 + 1 3 = 2 3

Two barrels are as much.

Just as much, of course.

After the first A pour, B has a volume of 3 2

The second time, B poured out 3 2 of 1 3, which is 1 2, so both of them are the same number.

As much as I am, I'm in the sixth grade of elementary school, and I'll do it!

After pouring half of the oil into the barrel B, the ratio is: 1:3

Then 3*1 3=1

1+1=2(a).

3-1 = 2 (B).

There are as many in barrels A and B, let the oil in barrels A and B be x, after the first pouring of oil, and after the second pouring of oil, the oil in barrel B is x

a=-1

Analysis: The square roots of positive numbers are opposite to each other.

The sum of two numbers that are opposite to each other equals 0

2a-1)+(a+2)=0

2a-1-a+2=0

a=-12a-1=2×(-1)-1=-3

a+2=-(-1)+2=3

That is, the square root of this positive number is 3

3) 2=9, so this positive number is 9

The square of (2a-1) is equal to the square of (-a+2), and the solution is a=-1, a=1

2a-1=-(-a+2)

a= -1 uses the square roots of a number to be the opposite of each other.

There are no two cases.

The square root of a positive number is the opposite of each other.

2a-1+（-a+2）=0

a+1=0a=-1

A = 1 or -1, these two numbers are either equal or opposite.

（1） （b+c-a）/2

3) This question is very strange If you define a new algorithm, the answer is the square of b (4) Let the call be x minutes, then there are: 20+< solve x>200 So when the talk time is greater than 200 minutes, choose a card, and when it is less than 200 minutes, choose B card.

1. C = 1 2(b+c - a);

2.4 * (1331 open to the 3rd power) square.

3. a*a -2ab + b*b

4.Assuming x minutes of use per month, 20 + = solution gets x = 200 minutes.

In other words, when the monthly usage time is less than 200 minutes, the B card is cost-effective, and when the monthly usage time is more than 200 minutes, the A card is cost-effective.

(1) A B C = (a + b + c) 2 C = (A + B + C) - (A B ) = (a + b + c) 2 - a = (b + c - a) 2

2) Because the volume is 1331 cubic decimeters, the side length is 11 decimeters, and the area of a surface is 121 square decimeters, which is cut into 3, that is, cut twice, increase 2 2 surfaces = 121 2 2 = 484 square decimeters (3).

The volume remains unchanged, and the edge length is set to x

x³=5×10×20=10³

x = 10 edges with a length of 10 cm.

5 10 20 = 1000 (cubic centimeters).

A: Yes 10 cm.

Solution: Set the edge length to x cm.

According to the meaning of the question, the equation is listed.

x cubic = 5 * 10 * 20

x cubic = 1000

Open the cubic side. x=10

It has been tested and is in line with practical significance.

Answer: The edge length of the iron cube cast into a cube is 10 cm.

Actually, it's not that hard.

3x+5y=2x+3y+2

x+y=2So, x=2, y=0, substituting k=4

Children who have been harmed by Chinese education.

Math is useful!! Ay! In addition to being used for exams.