Shanghai Science Edition mathematics basic training 8.5 expand space answer

Shanghai Science Edition mathematics basic training 8.5 expand space answer

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Shanghai Education Edition! P87 third question!
Shanghai air pollution index and air quality data in February 2008
Good air quality, light pollution
Days 6 20 2
(1) Please estimate how many kinds of air quality in Shanghai in one year (365 days)

February is a total of 6 + 20 + 2 = 28 days
In 28 days,
6 / 28 ≈ 21.43% of the air quality was excellent
Good air quality accounted for 20 / 28 ≈ 71.43%
2 / 28 ≈ 7.14% of the air quality was slightly polluted
Then,
In 365 days of the year, 21.43% + 71.43% = 92.86% of the air quality is good or above
A total of 365 x 92.86% ≈ 339 days

When Xiao Ming calculated the sum of the inner angles of a polygon, the sum of the inner angles was 1680 degrees. When he found that he was wrong, he checked again and found that he was missing an inner angle. He asked how many degrees was the inner angle? What was the sum of the inner angles of the polygon?

Calculation formula of inner angle sum of n-polygon: 180 * (n-2)
And each inner angle is less than 360 degrees
When n = 11
The sum of internal angles is 1620 degrees, which is impossible
When n = 12
The sum of the inner angles is 1800 degrees. Maybe, the inner angle is 120 degrees, which is a 12 sided shape
When n = 13
The sum of internal angles is 1980 degrees. If it is a convex polygon, it is impossible. If it is not a convex polygon, it is possible. The internal angle is 300 degrees
It is 13 sided

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A detailed explanation of the problems related to the system of linear inequalities in one variable
If the system of inequalities {3x-1 ≥ a + 1}
{2-x＞1-2a ②
If there is no solution, find the range of A

3X-1≥a+1
X ≥ a + 2 / 3 triple
(2): 2-x > 1-2a
2-a+2/3＞1-2a
　a＞－1/5

If 16 matches are connected end to end to form a rectangle (not including a square), the maximum number of rectangles with different shapes is ()
A. 1 B. 2 C. 3 d. 4

Let the number of matches used for the length of the enclosed rectangle be x, then the width is (8-x), then: X ＞ 8-x, X ＞ 4. From the meaning of the title, we can see that x ＜ 8, 4 ＜ x ＜ 8, and X is an integer. The number of matches used for the long side of the rectangle can be 5, 6, 7. That is to say, the maximum number of rectangles that can enclose different shapes is 3

If the solution set of the system x + 43 ＞ x2 + 1x + a ＜ 0 is x ＜ 2, then the value range of a is______ ．

If we solve the inequality system first, we can get x < 2x < - A, because the solution set is x < 2. According to the principle of taking the smallest from the same small, if 2 ≤ - A, then a ≤ - 2

In the "urban and rural cleaning project", an environmental sanitation team rents a number of vehicles with a carrying capacity of 8 tons to transport a batch of construction waste. If each vehicle only contains 4 tons, then 20 tons of construction waste is left; if each vehicle is full of 8 tons, then the last vehicle is not empty. How many vehicles does the environmental sanitation team rent?

If there are x cars, there are (4x + 20) tons of goods. From the meaning of the title, we get 0 ＜ (4x + 20) - 8 (x-1) ＜ 8, and the solution is 5 ＜ x ＜ 7. ∵ x is a positive integer, ∵ x = 6

Mathematics in the second grade of junior high school Volume II inequalities and systems of inequalities in one variable
Given that the root of the equation 3x + a = X-7 of relation x is a positive number, find the value range of real number a

3x+a=x-7
3x-x=-7-a
2x=-7-a
x=-(7+a)/2
Because x is greater than 0
So - (7 + a) / 2 > 0
(7+a)/2＜0
a＜-7

In the "urban and rural cleaning project", an environmental sanitation team rents a number of vehicles with a carrying capacity of 8 tons to transport a batch of construction waste. If each vehicle only contains 4 tons, then 20 tons of construction waste is left; if each vehicle is full of 8 tons, then the last vehicle is not empty. How many vehicles does the environmental sanitation team rent?

If there are x cars, there are (4x + 20) tons of goods. From the meaning of the title, we get 0 ＜ (4x + 20) - 8 (x-1) ＜ 8, and the solution is 5 ＜ x ＜ 7. ∵ x is a positive integer, ∵ x = 6