20 math questions in the first year of junior high school Questions Answers Analysis 20

31 pcs. Drawing is more complicated, and it is straightforward to reason:

1. Find the congruent triangle of the known triangle, the method is: first find the axis of symmetry, in the large square of 4 4 = 16 squares, there are two horizontal and longitudinal axes of symmetry in the middle; The 2 diagonals are the other 2 axes of symmetry. There are a total of 4 axes of symmetry.

Then through the two methods of symmetry and translation, all congruent triangles are found.

2. In the figure, there are 4 4 grids, d1e1f1 (including its vertices) occupies 3 3 grids, and the difference is 1 1 and 2 grids in the horizontal and vertical directions; Both the total grid and the triangle are squares. So, 1 triangle can be turned into 4 congruent triangles by symmetry and translation.

3. There is 1 d1e1f1 in the original figure, 1 is obtained by translating upwards, 2 are obtained by translating to the right, a total of 4 (including 3 new ones), these 4 triangles are symmetrical up and down, left and right according to the horizontal and vertical, diagonal 2 types of symmetry axes, 2 4 = 32 are obtained, 1 is subtracted from the original diagram, and 31 new congruent triangles are found.

If you just observe, you can count them.

The current diagram can be moved one to the right, one to the top, and one to the right, and there can be three. There are also three symmetry diagrams.

Therefore, there are a total of 6*4=24 congruent point triangles.

Cars A and B depart from A and B at the same time and travel in opposite directions, A travels 50 kilometers per hour, B travels 40 kilometers per hour, and A arrives at the midpoint 1 hour earlier than B. How many hours does A reach the midpoint?

A x hour to reach the midpoint.

50x=40(x+1)

10x=40

x = 4 A 4 hours to reach the midpoint.

Go to the bookstore and buy a book on Olympiad problems... The kind with the answer will do.

A 6 weeks + B 6 weeks = 10,000 (1).

A 4 weeks + B 9 weeks = 10,000 (2).

1) 3- (2) 2 Get A 10 weeks = 60,000, A 1 week = 10,000, substitute B 1 week = 4 150,000.

The ** of B for a week is less than the ** of A for a week, so choose Company B.

The decoration cost of company A and company B is x y million yuan respectively, and the system of equations is 6 (x + y) = 4x + 9y =

The solution is x=4 15

y=3/5

Solution: (1) The 64th square, the base should be 2, the index is 63, so it is 2 63;

2) Let x=1+2+2 2 + 2 63 multiply both sides of the equation by 2 at the same time to get 2x=2+2 2 +2 3 + 2 64

Get x=2 64 -1

Solution: Let the number of rooms be x, then there are students (2x+49), 0 2x+49-4(x-1) 4, and the solution is 25 or 26

The number of students participating in the study was 99 or 101

No more than 100 people.

101 rounded.

A: The number of students participating in the study is 99

Hope to be adopted ...

1. If a is not a negative number, then the opposite of a - a must be (0 or negative) and |-a|=（ a ）

If -|x|=|-x|Then x=(0).

If -|a|=-a, then a( = )0, if a -a, then a( >0 if a, and |a|＞|b|Then the value of a+b is (positive number)2, A, B, C, and D four rational numbers discuss the size problem, A says: I am the smallest of positive integers, B says: I am the absolute value of the smallest, C says:

I am the opposite of half of A, and D says, "I am the reciprocal of C, can you write what they are?" Then arrange from smallest to largest.

In this question you typed "positive integer" into "positive positive number").

A = 1;The smallest positive integer is 1

B = 0;The absolute value of 0 is the smallest.

C = -1 2;Half of 1 is 1 2, and the opposite of 1 2 is -1 2 D = -2;The reciprocal of -1 2 is -2

D, C, B, A.

3. If the real numbers a and b are satisfied|3a-1|+|b-2|=0, find the value of a+b and the absolute value of 0

3a - 1 = 0，b - 2 = 0。Untie; Gotta :

a = 1/3，b = 2

a+b = 7/3

4. From the figure, it can be seen that b<0, a>0, | b | a |∴a+b | a |

b -a + a

b5, a part of |a|+b/b|b|+c/|c|6、|a|Fractions a+|b|b+|c|Fractions c+|abc|Divide the ABC (please list the molecular formula in the question or type it up in the way of **, it's my fault that I don't have god-like comprehension, ok?) ）

These questions are very basic and use your brain.

1) I didn't figure out who was the cheater 1∠2。。。Waiter Steak.

2）ab=ac+cb=5/3ac=20cmae=10cm ad=6l,de=4

3) 900 + 20 * s = 2000 + 15 * s + 1100 Xie Lao Changde s = 440

1.In the equation 2x+3y-4+2ky=0.

1) When k is the time, there is no term with y in the equation.

Solution: 2x+3y-4+2ky=0

2x+(3+2k)y-4=0

When 3+2k=0, there is no term with y in the equation, i.e., 3+2k=0

k=-3/2 .

2) When x=1, y=-2, find the value of k.

Substituting x=1, y=-2 into the original equation yields:

2-6-4-4k=0

k=-2, i.e. the value of k is -2.

Ahem, I'm sorry I only wrote the second question

2) When x=1, y=-2, substitute the original equation to obtain:

2-6-4-4k=0

4k=8k=-2

When x=1, y=-2, k is -2

The similar terms that are merged by the original form are: 2x+(3+2k)y-4=03+2k=0

k=-3/2

Substitution primitive: k=(2*1-2*3-4) 4=-2

Sample, this won't be, forgot to ask you what grade you are? Just ask me next time, haha.

k = -3 2 thi, so that the coefficient before y is 0