One question each for science and mathematics in the first year of junior high school, and one quest

Question 1: Find the average velocity of the aggregate. It takes the total distance of 400m (known) and the total time t (unknown, solve) according to the formula:

Average speed = total distance divided by total time. It is known that the first half of the time t1=10s, the second half of the time t2=200m 40=5s

Total time t=t1+t2=15s. So the velocity s=400m 15s=. So the answer is D

Question 2: Yes. This question emphasizes that the position of a point as a known straight line can be on a straight line, or outside a straight line, and there is only one

The first question is D, and the second question is correct.

The first half is known to be s=200m, t=10s. In the second half of the paragraph, we know that s=200m, v=40ms, you can find t=s v=200 40=5s, (the unit is omitted from the formula, and you should add it when you complete the solution.) ）。

Total average speed = total distance Total time = 400 (10 + 15) = 400 15 =, so choose d.

The second question is in-plane, two-dimensional, which should be a theorem in a book. You look through it. Yes, you can't find a counterexample.

It took 10s for the first 200m, 5s for the last 200m (200m 40), a total of 15s, and an average speed of 400m 15s=

Yes, it's just that the plane geometry is right, it's a theorem, and it's wrong in solid geometry.

The first question should be physics.

Option D, because half of the distance is 200 meters, the total time is 15 seconds.

Speed is the total distance traveled divided by the total time.

The second question is correct, if there is another straight line perpendicular to him, then because they (two lines perpendicular to the straight line) pass through the same point, they must coincide.

Senior brother can only help you get here.

1. The average speed is equal to the total distance and total time, which is 400m (10s+200m 40m s).

But there is also an easy way to average speed, at the same time: average speed = sum of the two speeds divided by 2, i.e. (v1 + v2) 2

For the same distance: average speed = 2v1v2 v1 + v2, that is, 2 20m s 40m s divided.

20m s+40m s=1600 60, so choose d2, right, the original words in the math book, absolutely correct drop

The average speed is the total distance traveled divided by the total time. 200 40 = 5 (seconds) 400 (5 10) = The second question is correct, because the second one cannot be found. The perpendicular segment from the point to the line represents the shortest distance from this point to the line, and since it is the shortest, there is only one.

Question 1. The time of the second half is 200 40 = 5s

The total time is 5+10=15s, the total distance is 400m, the average speed v=400, 15=

It is approximately the same as choosing the second question of D.

That's the topic of the first year of junior high school, it's all nonsense.

。。。This, it seems, I don't know.

The question may be copied incorrectly, and the answer may not be correct.

x+y)/3

(y-3z)/2=(x+3z)/5=[(x+y)-(x+3z)]/3-5)

(y-3z)/(2)The third equal sign is the equivalence theorem.

So x+y=y-3z=x+3z=0,y=3z,x=-3zx+y+z=z=14

2x+3y-5z=y-5z=-2z=-28, the proportional theorem can also be obtained by adding the numerator denominator of the next two fractions to obtain (x+y) 3=(x+y) 7 and thus x+y=0......

This problem is not difficult, first solve the ternary system of equations, find how much x, y, and z each get, and then substitute their values into 2x+3y-5z=? Can.

Solve the system of equations: (x+y) 3=(y-3z) 2(y-3z) 2=(x+3z) 5

x+y+z=14

The solution is x=-42, y=42, z=14. Substituting 2x+3y-5z=2*(-42)+3*42-5*14=-28.

Little brother, not a problem, you should think independently. There's no need to ask all the questions. Don't live up to your teacher's expectations.

1.(102+2006）*[2006-102）/2+1]=1004462

The formula for summing the difference series: (first term + last term) * number of terms 2 but the number of terms is not 952.

Just like 1-10, there are 10 numbers in total, which should be (10-1+1) numbers.

So a total of 953

Or you can simply use a formula to calculate it.

Let the first term be a1=102 and the nth term be an. Tolerance d=2.

then an=a1+2*(n-1).

Then there is 2006 = 102 + 2 * (n-1).

952=n-1

n=9532.Substituting x=2 into ax 3-bx+1=-4,8a-2b=-512ax-3bx 3=3 2(8a-2b)=-15 2, so the original formula =-15 2-5=-25 2

2、q=[(200-x)*30-4*

3. When x=166, p=16600, so w=16600 because if 167 people are arranged to make clothes, then 33 people are arranged to weave cloth, then 990 meters are woven and 167 people need 1002 meters of cloth to make clothes, because 990 meters is less than 1002 meters, so 167 people cannot be arranged to make clothes.

It's better to do your homework yourself.

The first question is minus 18, the second day is minus 13 4, and the third question x is greater than 3 and less than 4

The solution inequality group, written below.

It can be 0, and zero is also an even number, so the even number you are talking about already contains zero.

The power of zero of a negative number is also equal to 1, so n can be equal to zero in this problem.

n can be zero, zero is even, and is included in the formula n equals even, so it does not need to be taken out separately. The zero power of minus one is one.

In this topic, in fact, the discussion of n is odd or even or equal to 0, and it does not need to be so detailed.

Regardless of whether n is odd or even, 2n must be even, and 2n+1 must be odd.

We know that the number -1 is special, if it is an even power, then it must be equal to 1, if it is an odd power, then it must be equal to -1, and that's it.

So in fact, there is no need to be so clear.

As for when n takes 0, normally we n start from 1, and we don't count 0, which is basically common sense.

Including later, you will learn the number series, the nth term, there is no 0th term, it starts from 1, and it is considered the default.

1. To transport tons of coal, first use a car with a load of 4 tons to transport it 3 times, and the rest is transported by a truck with a load of tons. How many more times do you have to transport it to finish?

It will take x more times to finish.

x=7 takes 7 more rides to finish.

2. The area of a trapezoidal field is 90 square meters, the upper bottom is 7 meters, the lower bottom is 11 meters, how high is it?

Its height is x meters.

x(7+11)=90*2

18x=180

x=10 and its height is 10 meters.

3. A workshop plans to produce 5,480 parts in April. It has been produced for 9 days, and another 908 units can be produced to complete the production plan, how many units are produced per day on average in these 9 days?

An average of x per day was produced during these 9 days.

9x+908=5408

9x=4500

x = 500 x 500 per day for 9 days.

4. Two cars A and B traveled in the same direction from two places 272 kilometers apart, and the two cars were 17 kilometers apart after 3 hours. A travels 45 kilometers per hour, how many kilometers does B travel per hour?

B travels x kilometers per hour.

3(45+x)+17=272

3(45+x)=255

45+x=85

x = 40 B travels 40 kilometers per hour.

5. There are two classes in the sixth grade of a school, and the average score of mathematics in the last semester is 85 points. It is known that there are 40 students in six (1) classes, with an average grade of points; There are 42 students in Class Six (2), what is the average grade?

The average grade point is X points.

40*3484+42x=6970

42x=3486

x = 83 and the average score is 83.

6. After the school bought 10 boxes of chalk and used 250 boxes, there are 550 boxes left, how many boxes are there per box?

Average x boxes per box.

10x=250+550

10x=800

x = 80 average of 80 boxes per box.