Solve math problems in the first year of junior high school, solve math problems in the first year o

1. A certain steamer sails along the water for 3 hours and sails against the current for an hour, and the speed of the ship in still water is known to be a kilometer hour, and the current speed is Y kilometers an hour. How many kilometers did the ship travel?

3(a+y)+

3a+3y+

2。After a math test, three students, A, B, and C, talked together, and A said, "My score in this test is 98 points less than twice that of B." C said: My test score this time is more than half of B's.

52 points. Question 1: If it is known that B's score in this test is A, please use A to represent the results of A and C.

2: If the two numbers obtained by subtracting A's score and C's score from 97 are inverse to each other, ask: What is A's score in this test?

A: 2a-98;

C: 1 2A+52.

97-(2a-98)=-[97-(1/2a+52)]

97-2a+98=-[97-1/2a-52]

195-2a=-45+1/2a

2a+1/2a=195+45

5/2a=240

A = 96 A is: 2a-98 = 2 * 96-98 = 94.

The speed of the water is (a+y) kilometers per hour, and the reverse water is (a-y) kilometers per hour

Then the range is: 3(a+y)+

Simplification: 2(1) A is: 2a-98

C is: a 2+52

2) 97-(2a-98)+97-(a 2+52)=0Simplification:

a=96A: 2a-98=94

Solution: Suppose that the two meet for the first time after x seconds, and A runs one more lap than B, which is derived from the question.

9x-7x=400

Solution x = 200

What a nice name for the team! Analysis: First of all, it can be seen from the steel team that a loss is worth a point, and a win is x, which can be scored by the forward team

4+10x=24 So x=2 points, in order to ensure correctness, bring the obtained numbers into the Bright team, get: 5+9x2=23, in line with the actual points, and substitute into the Eagles to obtain: 7+7x2=21 in line with the actual points.

1) Total points = number of wins x 2 + number of lost games x 1

2) First to last row, 1

Let win a and lose b, then 2a = b, as long as the number of negative games is 2 times the number of victories, the result can not be found, so it can't.

4+10x=24 Pick the front team.

Analysis: Looking at the standings, it can be seen from the 8 rows of data: 1 point for a loss.

From which line can we find out the equality relationship? 1 2 3 4 5 6 7 Let a win count count x points, and depending on the equality relationship you choose, you can list the equation:

1. 10x+4*1=24

If the number of wins is x, then the number of losses is 14-x

1) 2x+14-x=x+14=total points.

2) According to the condition: 2x=14-x, x is not divisible, so the answer is no, 1

First row, 24-4=10x, x=2

x+14-x=x+14=total points.

(1) Total points = number of wins x 2 + number of losses x 1

2) As can be seen from the data in line 8, a negative game is worth 1 point;

From the first line, the equality relationship can be seen;

10*x+4*1=24

I was dizzy, and I felt like I wanted to sleep when I went to school and read.

Solution: The paper is folded along a straight line through p, so that the straight line a on both sides coincides, and the crease c c a and c passes the point p

Then fold the paper again through the point p, so that the crease c on both sides coincide to obtain a new crease b b over the p point perpendicular to c

a c (two straight lines perpendicular to the same line parallel).

The b(a) line segments are all long, so they may not intersect; (c) If P is on the long line of the repercussions of AB, the straight line cannot be drawn parallel to AB, but can only coincide; (d) Assuming that the straight lines are horizontal, as long as Li Yu draws the CD in the direction perpendicular to AB, it will not intersect.

Personally, I think that all 4 answers can make corresponding diagrams, if you have learned the knowledge of space vectors or space geometry, you can think of it.