15 points for a reward!! Urgent!!! Mathematics problems in the first year of junior high school

1).It takes X days for two engineering teams A and B to complete the project at the same time, which is derived from the title.

1 30 + 1 20) * x = 1, so x 12 = 1, so x = 12, that is, it takes 12 days for the two engineering teams A and B to complete the project at the same time.

2).A needs to pay 30 * 200 = 6000 yuan to complete alone, B needs to pay 20 * 280 = 5600 yuan to complete it alone, and A and B need to pay (200 + 280) * 12 = 5760 yuan for cooperation, so B alone construction costs the least.

Solution: (1) Let the total engineering quantity be s, the velocity of engineering team A is v1, and the velocity of engineering team B is v2, then the system of equations: s v1=30

s/v2=20

v1=s 30 v2=s 20

A and B construction at the same time, the total speed is v1 + v2 = s 30 + s 20 = s 12, so the number of days required n = s (s 12) = 12 (days) 2), the cost of A sole construction m1 = 200 * 30 = 6000 The cost of B alone construction m2 = 280 * 20 = 4800 The cost of joint construction m3 = (200 + 280) * 12 = 5760, so the choice of B team alone construction is the most cost-effective.

1) The sum of 1 divided by 1/30 + 1/20 equals 12 days to complete.

2) A alone construction costs 200 * 30 = 6000 yuan, B alone: 280 * 20 = 5600 at the same time (200 + 280) * 12 = 5760 yuan, so B alone to complete the province, the disadvantage is slow.

1) 1 (1 30 + 1 20) = 12 (days).

2) B is the most cost-effective to build alone, because as long as 5600 yuan, this price is the cheapest.

Divide 1 by 30 and 20 and 12 days and the second one is also very simple Do it yourself.

2-kxy-3xy-3y 2-8=x2-(k+3)xy-3y2-8 does not contain xy, then k+3=0, k=-3 because the polynomial (a-4)x to the power of 4 - (5+b)x to the power of 5 + the power of x to the power of 2 -3 is about the quadratic polynomial of x, which means that the coefficients of the 4th power of x and the 5th power of x are 0

Therefore, it can be obtained: a-4=0,5+b=0.

So: a=4, b=-5.

a-4)x to the power of 4, which can be denoted by: (a-4) x 4. 1

1.What about k in a polynomial?

2..a=4,b=2,a+b=6

0 and ≠-1, (-m+1) polynomial.

m= 1, 2nd order polynomial.

m>0 and ≠1, (m+1) polynomial.

Solution: Suppose the distance is s

The speed of the car is 20m s

2s=20*4+340*4

s=720(m)

Answer:..

72k/h=72/

Sound walking: 340*4=1360m

Car walking: 20*4=80m

The sound is more than a person, and the distance from the location of the sound to the valley is 2 times (you can draw a picture yourself to see the .......)）s=（1360-80）/2=640m

72 km/h = 20 m/s.

20*4=80 meters.

340*4=1360 meters.

1280 2 = 640 meters.

Set the reverberation to be heard when you move away from x

72km h=20m s, you can quickly know that 2 (x+4*20)=340*4+4*20

x=640

(1) Solution: If x cars are set to transport B vegetables, then 8-x x + cars are to be transported to C vegetables

x+x=2∴8-x=6

Answer: 2) Solution: If the car transporting vegetables A is x, then the car transporting vegetables B is 8-x 500*2x+700*1(8-x)=65001000x+5600-700x=6500

1000x-700x=6500-5600

300x=900

x=3∴8-x=5

Answer:..

Brother, it's been almost two months since I graduated from my senior year of high school. I've almost forgotten what I've learned, haha.

Question 1: Since the common solution is x=1, 1+b=a+3, so b=a+2, so (a-1)x1, x<1; a<1, x>1; a=1, there is no solution.

Question 2: According to the formula, we can get a(b-3)x+b, so it becomes bx+b<0, b(x+1)<0; And then because K1>K2, B-3>-3, B>0

So x+1<0; x<-1

Give it points, it's hard enough to get 5 points.

Are you sure it's the first year of junior high school、、、

1. The common solution of y=x+b and y=ax+3 is x=1, and the calculation is obtained by substituting x, 1+b=a+3, that is, b-3=a-1

x+b ax+3 can be transformed into x<(b-3) (a-1), then the solution set is x<1

2. From the problem, it can be seen that x>a, and x<1, if there are only 3 integer solutions, then there are only 3 solutions, 0, -1, and -2, so the range of a is:

3k2,

Solution: Simplifying the original formula = kx -2x +2 3 y 2 -3 2 x -1 3 y 2

k-7/2 )x +1/3 y^2

As can be seen from the problem, when x = 2 and x = -2, the values of the algebraic equation are equal.

So, (k- 7 2)*2 = (k- 7 2)*(2) so k= 7 2

First, we bring x=-2 and y=2 3 into the equation to get -2k+7+12 27;Then substituting x=2 and y=2 3 into the equation gives 2k-7+12 27, and finally makes -2k+7+12 27=2k-7+12 27, and solves k=7 2

The answer is 2 7

Multiple choice questions will not.

Multiple choice: Because -x+2y=6, x-2y=-6

Original formula = 3*(-6)*(6)+5(2y-x)+6