Math problems in the first year of junior high school. Simple. Correct answers

1.Solution: If the teacher uses x hours, then the students use (x + hours.

4 (x+x=distance=40x=40*km).

A: The distance from the school to the destination is 10 km.

Solution: The price of X copies is the same.

x=1200

A: The two charges are the same when printing 1200 Fen.

2) When printing 1500 copies, factory A charges = yuan).

Factory B charges = yuan).

Answer: Factory A charges less.

eof=（100+40）/2=70°

eof=n/2

Since OE bisects AOC, EOC=1 2 AOCOF divides BOC, so COF=1 2 BOCEOF= EOC+ COF=1 2 AOC+1 2 BOC=1 2 AOB

When aob=n, eof=n 2

1.Let the distance be s, according to the meaning of the question: s s

Solution: s 10 (km).

2.<1> set x copies, according to the title:

Solution: x 1800

So pick the first one.

3.I can't draw a picture for you, so I'll give you the answer.

2>（360°-n°）/2

To explain: the circumferential angle is 360°, and since AOB = N°, and OE bisects AOC and OF bisects BOC, the degree of EOF is 360° minus half of AOB.

Oops, I didn't expect to answer math ...... here

I'm really tired ......

1. The distance from the school to the destination is x kilometers.

x/4-x/40=

Solve x 10 km.

2. Question: (1) When the school prints how many copies of the program list, the cost of the two printing houses is the same.

When a school prints x copies of the program, the cost of the two printing houses is the same.

The cost of factory A is 900+

The cost of factory B

So 900+

Solve x 1200 copies.

2) The school wants to print 1,500 copies of the program list, which printing house will pay less?

The cost paid by the selection plant is 900+ yuan.

The cost paid by the B selection plant is yuan.

Therefore, the cost of the first factory is less.

3. (1) Because OE divides AOC equally, OF equalizes BOC.

COE 1 2 AOC, COF1 2 BOC if AOC=100°, BOC=40°

So: eof= coe- cof=1 2 aoc-1 2 boc=1 2*100-1 2*40=30°

If aob=n°, find the degree of eof and explain why.

Because OE divides AOC equally, OF equalizes BOC.

aoe＝1/2∠aoc，∠bof＝1/2∠bocaob=n°

So eof aob- aoe+ bof n-50+20 (n-30)°

There are so many questions that only offer a reward of 20 points, and it's too nerve-wracking not to do it.

1. If the distance is x, then x 4 = x 40 +, x = 102, (1) the cost of the two printing houses is the same when printing x copies of the program.

then, we get x=1200

2) Factory A cost:

Factory B cost: So the cost of factory A is less.

3，∠eof=30 °

eof=n°/2

Because eof= boc2+ aob- aoc2

Analysis and Answer: There are only two ways for students A and B to travel: cycling or walking, because they travel alternately, from the statistical point of view:

The distance traveled by A + the distance walked by A = the distance traveled by B + the distance traveled by B.

A's riding time + A's walking time = B's cycling time + B's walking time.

Arrive at the same time) the distance traveled by A on a bicycle + the distance traveled by B on a bicycle = the whole distance.

Assuming that the whole distance is 100 kilometers, and the distance traveled by A is x kilometers.

Then the equation is available.

100-x)/3+x/15=(100-x)/15+x/5

100/3-1/3*x+1/15*x=20/3-1/15x+1/5*x

1/5*x+1/3*x-1/15*x-1/15*x=100/3-20/3

2/5*x=80/3

x=80/3*5/2

x=200/3

i.e.: x=66 and 2 3).

The time for the complete journey of line A is (100-200 3) 3 + 200 3 15 = 140 9 (hours), i.e., 15 and 5 9 hours.

The average speed of the whole journey is: 100 140 9 = 45 7 (kmh), that is: 6 and 3 7 km/h.

It can also be assumed that the whole distance is in other data or letters, and the average speed remains the same, except for the time difference, which is still 45 7 (km h), i.e., 6 and 3 7 km h.

Question 1.

Let the numbers be z

10+x=?

100x+200+10y+z=？

When you tell her to count. Subtract 200. The hundredth digit is x, the tens digit is y, and the single digit is z.

ax+b）*(x+2)=x^2-4

ax^2+2ax+bx+2b=x^2-4

then a=1 2a=-b b=-2

then the desired is 1

What is the first unit? Got this problem?

1. You can look at it the other way around. The single digit of the final result must be the third number, and the second number above the tenth. Remove the number of 10 and divide the rest by 5, subtract 4, and divide by 2 to get the first number.

2、（ax+b）*（x+2）=ax^2 +（2a+b）x +2b=x^2-4

So b=-2 a=1 gives a b=1

The first and three numbers are a, b, and c

a*2+4)*5+b]*10+c=(a+2)*100+b*10+c

Then the three numbers a, b, and c can be seen at a glance.

2. (ax+b)*(x+2)=x 2-4

a=1 b=-2

a^b=1

1. Reverse thinking; Because step 5 is multiplied by 10, we know that the third number must be the single digit of the final number; Subtract the third number from the final number and divide it by 10, then the remaining single digit is the second number (because the number obtained in steps 1 to 2 is an even number multiplied by 5 and then more than ten digits), subtract the second number from this number and divide it by 5, and then subtract 4 by 2 to get the first number.

2, ax 2+(2a+b)x+2b=x 2-4 is true, then a=1; 2b=14 (i.e., b=-2); 2a+b=0 constant establishment; Get a=1, b=-2

1.Assuming that these three numbers are a, b, and c, then the question is derived:

a*2+4）*5+b]*10+c

10a+20+b]*10+c

100a+200+10b+c

100a+10b+c+200

Mr. Wang subtracts 200 from your result, and the hundred, ten, and single digits of a three-digit number you get are the three numbers you want.

Xiao Ming's father rode a bicycle with Xiao Ming on the highway at a constant speed, when Xiao Ming noticed the number on the roadside milestone for the first time, he found that it was a two-digit number and the sum of its two numbers was 9, just after an hour, he found that the number on the roadside milestone happened to be the first time he saw the single digit and the ten-digit number reversed, and after another 3 hours, he found that the number on the milestone was more than 0 in the middle of the two-digit number he saw for the first time, do you know what is the speed of Xiao Ming's father riding a motorcycle?

Solution: 1) Use the formula containing x and y to represent (x ten y) the first notice of a roadside milestone.

When the number is seen, what is the sum of the two digits of these two digits (x+y = 9) After an hour, he finds that the number on the roadside milestone is (10x+y) Another 3 hours have passed, and he finds that the milestone number is (100y+x) From the second time he saw the number on the milestone to the first time he saw the number on the milestone he traveled was (10x+y-x-10y), and from the third time he saw the number to the second time he saw the number, he traveled (100y+x-10x-y), the relationship between the two distances is (1:3).

2) According to the question, list the corresponding equation as ().

x+y =9

10x+y-x-10y):(100y+x-10x-y)=1:33)

x=7y=2

4) Calculate the speed at which Daddy rides a motorcycle is (45).

Write out the process in full, and understand it in detail!

Points are not a problem, some are points.

By the way, the following formula is simplified.

x+2)(x-2)+(x-2) +(x-2) quadratic +(x-4)(x-1)x-4+x -4x+4+x -5x+4

3x²-9x+4

No solution, you girl, do you know what the speed of Xiao Ming's father is on a motorcycle?

Xiao Ming's father rode a bicycle and took Xiao Ming to drive at a constant speed on the road

Simplify. x+2)(x-2)+(x-2) to the second power of +(x-4)(x-1).

x quadratic - 4 + x quadratic - 4x + 4 + x quadratic - 5x+4

3 x quadratic - 9x+4

Figure 1 gets b>a

Figure 2 gets d>c

Figure 3 should be synthetic, because b+c>a+d, so b-a>d-c because a+b=c+d

=2b>2d, b>d is combined to get b>a>d>c

Do you understand, ask for praise.

From 1 to Ba + C + 2D, so B > D, and then combine 3 to get A

When x = 2, the value of ax to the fifth power + bx to the third power + cx-5 is 8, then ax to the fifth power + bx to the third power + cx = 13

When x = -2, the polynomial = -ax to the fifth power - bx to the third power - cx-5

ax to the fifth power + bx to the third power + cx) -5

Bring in specific values.

Discover patterns. Make up a knowing whole.

Know-18

The title is about the range of values of A, that is, the possible values of A. and not a unique value. You can give a lot of examples in that way, such as a = 40 degrees, b = 30 degrees, c = 110 degrees, isn't it not the smallest angle?

So the range of values can't be reversed like you do, and the argument that the question requires proof is that a can reach those ranges, not necessarily that value.

A may be between 0-60 degrees, for example, a = 40 degrees, b can be 60 degrees, so c is 80 degrees, and a may be the smallest angle.

However, if A is greater than 60 degrees, the sum of the remaining two angles can only be less than 120 degrees, so that one of the angles must be less than 60 degrees, and A is not the smallest angle, so A cannot reach more than 60 degrees.

Got it?

Decompose the factor. 3(x

2y)^2+9(2y-x)

3(x-2y)^2-9(x-2y)

Extract the common factor.

3(x-2y)(x-2y-3)

Simplification is the first in the evaluation.

3x+2)(

x-2)-5x(x-1)-(2x-1) 2, where x=1 3

9x^2-4

5x^25x

4x^24x

9x1, top and bottom margins, and left and right margins are all known.

Then the length and width of the actual print can be obtained.

Length. Width. b-5

Thus the actual area is (

2、x^2+3x+5=7

Tease to x 2 + 3 x = 2

Get 3x 2+9x=

3x^2+9x-2=6-2=4

3. The answer to the factorization of a 4-4ab-5b 2 cannot be (a+b)(a-5b), you get a 2-4ab-5b 2 by taking the pure (a+b) (a-5b).

A 2-4ab-5b 2 has a maximum order of 2, with a total of three items.

That's why it's called a quadratic trinomial.

You must have typed the question wrong.

As for one sentence summarizing the above method of dismantling:

Make up two perfect squares and use a 2-b 2=(a-b)(a+b) to factor them.

2)、x^2-6xy+5y^2

x^2-6xy+9y^2)-4y^2

x-3y)^2-(2y)^2

x-5y)(x-y)

My brain cells!!