200 high marks for math problems are given. To analyze

Set up the purchase of Yang tree and willow tree, respectively X plant, Y plant.

Yes. 3x + 2(400-x-y) +3y = w+ +=90

Simplify.

x+y+800=w

90 is 3x + y >=500 and the number of poplars and lilacs is required to be purchased.

then there is 400-x-y=x

Simplification to get 2x-400=y into the previous two formulas, get.

x+2x-400+800

3x+400=w (multiply both sides of this equation by 5 3 to get 5x=w-2000 3).

3x+2x-400

5x-400>=500

Substituting 5x=w-2000 3 into the above equation is obtained.

w-2000/3-400>=500

So get w>=900+2000 3 (the result is your own calculation).

There are x poplar trees.

Omit in between. Solution: 200>x>100 (1)w=(3+2)x+3*(400-2x).

1200-x

It can be seen from (1).

1000

Let poplar be x because the number of poplars is equal to that of lilac trees.

Inequality 1: 2x 400 launched x 200 and 200 due to the air purification index of the residential complex two years later and not less than 90 can be obtained inequality 2: launched x 100

100 x 200

Available from known.

w=3x+2x+3×(400-2x)

w=1200-x

Substituting 100 x 200 yields: 1000 W 1100 Okay give it points.

Launch 5x+2y 900 (1), and 2x + y = 400 (one), launch y=400-2x, and replace it with (1) to get x 100 (2).

w = 3x + 2x + 3y = 5x + 3y = -x + 1200 (two), substituting the two formulas into w 1100

and from (1) get 2x 400, that is, x 200 (3) and (3) get w 1000 from (3) generation (2).

Therefore, the value range of w is 1000 w and 1100

Please do the math yourself.

A good teacher will only give you some pointers.

Let's buy a poplar tree for x plants. , the number of lilac trees is x.

Let the willow tree be the Y tree.

You should know how to do it according to the prompts.

** w=...5x+3y ①

Air purification index 90 ...5x+2y ②

400 saplings = 2x+y

From the equation and w=....x

Get 2x 400 from

It is obtained by taking the y in with x and bringing in .

x 100 answers.

Please see others for the process.

If you don't understand, I'm oh!

This kind of question, don't expect one yuan at a time.

Plus, you're just a 100-point bounty.

Topic 1 If x 2, simplify [x-2.]Note that this simplification of x-2 is an absolute value. 【 Parentheses representing absolute values.

x-2】=2-x

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a=4, b=8

a-b)÷ab=（-4）÷32=-1/8

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