Math problems, I don t understand, ask for help! Urgent

1) y=20x( +11 60( (60 x 100)2) Since it is a one-time function, when x=100, there is a maximum profit of 578.

y increases as x increases. So x=100

y=2000+

x: greater than or equal to 60, less than or equal to 100) and 21x greater than 2660 to obtain x greater than x=86

y=795 yuan.

Solution: (1) The profit of selling each newspaper is yuan, and if it cannot be sold, it will lose yuan per copy, and about 20 * 100 + 11 * 60 = 2660 newspapers can be sold in a month, and the relationship between the profit y and x is:

When 31*x>2660, that is, x>2660 31;

y=when 2000<31*x=<2660.

y=31*x*

From the above, it can be seen that when x=2660 3, the profit is the largest, is: y=

This problem is a process of finding partial derivatives....Detailed and complete process rt ......Hope it can help you solve the problem in your mind.

Total salary: (55 yuan-500 yuan 5%) 10% + 2000 yuan + 500 yuan = 2800 yuan.

Actual receipt: 2800 yuan - 55 yuan = 2745 yuan.

Solution: Set the salary to be X yuan, and pay the tax Y yuan.

When x 2000, y=0

When 2000 x 2500, y=(x-2000) 5%=, at which point y 25

When 2500 x 4000, y=25+(x-2500) 10%=, 25 y 175

x＞2500

require, then x=2800

2800-55=2745 yuan.

The salary is 2,800 yuan, and the actual salary is 2,745 yuan.

A classroom is 8 meters long, 6 meters wide, and 6 meters high. Now the area of the walls and ceilings, doors, windows and blackboards to paint the classrooms is 22 square meters, and the average kilogram of paint per square meter is used.

8+6)*2*kg.

The surface area of the box is equal to.

Length x Width + Length x Height + Width x Height) x 2

It is the area of six polygons in total.

Because it's a house, the ground can't be counted, so it's less than a length x width area, so it is.

Length x Width + (Length x Height + Width x Height) x 2 = Area of 5 Faces 8x6 + (square meters.

Then minus the area of windows and chalkboards is 146-22 = 124 square kilometres.

I don't know if it's clear enough to say this!

Find the surface area first:

124 square meters.

124 kg.

Painting classrooms requires 31 kg of paint.

Solution: The area at the top of the classroom 8 6 = 48 (m) The area of the four sides of the classroom (8+6) 2 98 (m) The area of the classroom that needs to be painted 48+98-22 = 124 (m) The total amount of paint needed to paint the classroom = 31 (kg).

A: A total of 31 kilograms of paint was required to paint this classroom.

Find the surface area first:

124 square meters.

124 kg.

Find out the area of the wall and ceiling first

Four walls (minus the area of doors, windows, and chalkboards): 2 (8 x + 2 ( -22 = 76.)

Ceiling: 8x6 = 48

How many kilograms of paint do you need?

x 124 = 31

First of all, it is clear that the floor of the classroom does not need to be painted, so it is necessary to find the surface area of the rectangular without a bottom surface that is 8 meters long, 6 meters wide and 6 meters high, and then subtract the area of doors, windows and blackboards.

8 6+(8 sq.m.)

146-22 = 124 square meters.

124 kg.

(8 plus 6 plus 6 answers minus 22 and multiply.) Miss Jianghu is really a good person to ask, if you have any questions, I will help you answer them in time, and I also implore the eldest lady to accept if she is satisfied, and give a good review if she is not satisfied. Thank you.

For example, if you look at the straight line x+y=0.

He divided the plane into two parts, the points in those two parts.

The substitutions are x+y>0 and x+y<0, respectively

Just find two points and substitute the equation to know who is which inequality, for example, (5,0) is x+y>0, so the region where he is located is x+y>0, and the other side of the fiber is extreme.

x+y<0 In the same way, you draw x=3 x-y+5=0 and find the two ranges in the same way.

We won't talk about it separately.

Make a diagram first, and then find the shaded areas within the intersection.

The three intersections are (, 3,-3) and (3,8).

According to the principle of equal volume.

The forged piece of steel is x meters long.

x=x=

The forged square steel is x m x m x = long

The forged square steel is x meters long.

x=x=

Solution: Set each pencil to be $ x, notebook to be $ y, and fountain pen to be $ per pen.

20x=2y, so y=10x, 6y=z, so y=1, 6z, substituting z=60x

1 pen and 1 notebook can be bought for (y+z) x=(10x+60x) x=70

1 notebook = 10 pencils.

1 pen = 6 notebooks = 60 pencils.

60 + 10 = 70 pencils.

If the pencil ** is x yuan, the notebook ** is y yuan, and the pen ** is z yuan, then 20x=2y launches y=10x

6y=z=60x

So if you have z+y=60x+10x=70x, you can buy 70 pencils.

20 pencils cost the same as 2 notebooks.

60 pencils cost the same as 6 notebooks.

The price of 6 notebooks is the same as the price of 1 fountain pen.

In other words, the price of 1 fountain pen is the same as the price of 3*20=60 pencils, and the price of 20 pencils is the same as that of 2 notebooks.

So 1 notebook is the same price as 10 pencils.