Two junior high school math problems and two junior high school math problems

The sum of the inner angles of the sides is (n-2)*180, and the inner angles are less than 1801125=6*180+45, so the sum of the undercounted inner angles is 180-45=135

The result is a 7-sided shape.

2.The center of an outward circle.

The sum of the inner angles of the edge is 180 (n-2), 1125 = 180 * 7-135, so this inner angle is 135 degrees and is a 9-sided shape.

2.Diagonal intersection.

1:135 degrees 9-sided.

2: The center of the circumscribed circle.

Question 2: At the intersection of the angular bisector of the four corners.

The first: 135 degrees 9 sides.

The second: the center of the circumscribed circle.

1.If the contestants are x, the number of games that any one player needs to participate in is (x-1), and the total number of games to be played by all players is x(x-1) 2

The score of each game is 2 points, and the total score of all players is 90 points, which can be listed as follows: 2 * x(x-1) 2 = 90

The solution yields x=10 or -9 (rounded).

That is, there are 10 players, and each player must go through 9 matches. Player A scored 18 points, obviously won all 9 games, and was definitely the champion.

2.If there are x rooms on the second floor, then there are (x-1) rooms on the first floor, 2 people live on the first floor (x-1), and (x 2-x) people live on the second floor.

x-1) 2+(x 2-x)=36, the equation is reduced to: 2x 2-3x-35=0

That is: (x-5)(2x+7)=0

The solution yields x=5, x=-7 2 (rounded).

So choose A

1.The total score of all players is 90 points, and the number of matches is 90 2 = 45 times

If the number of players is x, then.

x(x-1) 2=45, x1=10, x2=-9 (rounded), so the number of players is 10

The winner of each game is worth 2 points, and each player has 9 games, and each player can score up to 9 2 = 18 points, and player A has a total of 18 points in this game, and player A will definitely become the champion.

2.There are x rooms on the second floor, (x-1) on the first floor, (x-1) on the first floor, (x-1) for 2 people, and (x 2-x) on the second floor.

There are 36 people staying in the "can be listed (x-1) 2 + (x 2-x) people, you can list the equation, solve the equation can be solved, pay attention to the actual meaning.

Trade-offs for row values

Solution: There are x rooms on the second floor, according to the meaning of the problem (x-1) 2+(x 2-x)=36, and the equation is simplified as: 2x 2-3x-35=0

That is: (x-5)(2x+7)=0

The solution yields x=5, x=-7 2 (rounded).

Therefore, choose A to get extra points.

Suppose there are x players so one player wants to participate in x-1 games, there are x players in total, and because this is counted as exactly one repeat, so x(x-1) 2=90, x=10, a total of 10 players 18 2=9, he wins 9 games, that is, all the games, and it is possible to become the champion.

There are x rooms on the first floor and (x+1) rooms on the second floor. The first floor has x square beds, the second floor bed (x+1) square, and the empty room has (x+1) beds. x square + (x + 1) square - (x + 1) = 36 x = 4 4 + 1 = 5

There are 5 rooms on the second floor.

1 Pi does not have a fixed value of filial piety, so it is used to indicate the elimination |3-Pi|=3-π

2 |c|=4 9 so C. C is + -4 9 So 1 C=+-4 9

Question 1: If the speed of B is x, then A x+7 is set, and when t xt=10 (x+7)t=24, t=2 x=5, that is, A, 12km, H, B, 5kmh

Question 2: The ratio of the speed of the downhill road is 3:4:5 respectively, I don't understand.

2x^2+my-12+nx^2-3y+6=(n+2)x^2+(m-3)y-6

Because they and do not contain nano-cleft masses have x,y,so.

n+2＝0 n=-2

m-3＝0 m=3

mn=3*(-2)=-6

Similarly: 2x +ax-y+6-2bx 2+3x-5y-1==(2-2b)x 2+(a+3)x-6y+5

Because their value has nothing to do with the value of the letter x, the source of the hand.

2-2b＝0 b=-1

a+3＝0 a=-3

So, here you go.