Find math problems difficult in the second year of junior high school

1.The functional relationship between the total cost price of a certain Nissan gloves Y yuan and the daily output of x pairs is y=5x+40000, and the factory ** of gloves is 10 yuan per pair.

2.A unit is in urgent need of a car, and they are ready to sign a monthly car rental contract with two taxi companies, A and B. For every X km of the car, the monthly fee of Company A is Y1 Yuan, and the monthly fee of Company B is Y2 Yuan, and the image of the relationship between Y1 and Y2 respectively and X is shown in the figure

1) What is the range of distance traveled per month, and is it cost-effective to rent a car from Company B?

2) What is the same amount of distance traveled per month and the cost of renting a company car is the same?

3) If the estimated distance traveled by this unit is 2300km per month, then which car is the best car to rent for this unit?

Not losing money means that the total income per day is greater than the cost.

There is the following inequality: 10x>y, i.e., 10x>5x+40000, and the solution is x>8000

So at least 8000 per day

You go and buy an Olympiad book, the second year of junior high school, and the one on it is larger. I have it at home. I feel like I can't finish watching it, let alone telling you!

The finale of primary functions, equations, the Pythagorean theorem and geometry.

Congruent triangles.

Axisymmetric multiplication and division of integers and factorization.

At first, it may be a bit of a problem for congruent triangles.

But do more and you'll find the trick.

It's going to be simple.

I think put. That kind of theorem.

What a corollary?

The inverse theorem, these are a bit of a mess.

You have to turn your back to it.

Those what. Special parallelograms.

Properties such as rectangles, diamonds, squares, etc., are judged to be defined by opening their eyes and dots, and these should be learned.

Because by the ninth grade, these will be used a lot.

Those comprehensive questions should be quite difficult.

Sue: Primary function, inverse proportional function.

There are also quadratic functions.

Solution: (1) Set: rapeseed oil ** is x yuan kg when two people buy m times, ** is y yuan kg when two people buy n times, the average ** of A is:

5xm+5yn) (5m+5n)=(mx+ny) (m+n) yuan kg.

When m=n, the average price is: (x+y) 2 yuan kg.

The average ** of B is:

50m+50n) (50m x+50n y) = (m+n)xy (nx +my) yuan kg.

When m=n, the average price is: 2xy (x+y) yuan kg.

2) The difference between A's average** and B's average** is:

mx+ny)/(m+n)- m+n)xy/( nx +my)=[ (mx+ny) (nx +my)- m+n) (m+n)xy]/ (m+n) (nx +my)

mn(x²+y²)+m²+n²)xy-( m+n) ²xy]/ (m+n) (nx +my)

mn(x²+y²)-2mnxy] / (m+n) (nx +my)

mn(x²-2xy+y²)/ (m+n) (nx +my)

mn(x-y) ²/ (m+n) (nx +my)

m＞0 n＞0 x＞0 y＞0 (x-y) ²0

mn(x-y) ²/ (m+n) (nx +my) ≥0

That is: the average price of A - the average price of B 0

The average price of A The average price of B.

When x=y, the average price of A and B is equal, that is, the oil price of rapeseed oil is equal and unchanged every time they buy rapeseed oil.

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