Question 1: Learn more. According to the first sentence of the first paragraph: when the traffic lights turn red.
We will stop driving or crossing the road. It can be seen.
So choose a small question 2 to learn more. According to the first sentence of the third paragraph: Of all the light we can see, red has the longest wavelength, so its scattering is the weakest.
It can be seen. So choose B.
Question 3: Guess the meaning of the word. If the wavelength is long, the scattering is short.
So choose C- question 4 for details. According to the first sentence of the last paragraph: using red light can help drivers in other areas see the light, which helps drivers stop in time.
So choose C-question 5 to summarize the comprehension questions. According to the question raised in the first paragraph of this article: Why do traffic lights use red instead of other colors? So we choose the test center C: popular science essay reading.
2. In order to measure the height of a mountain, select ABC3 points on the same straight line at the bottom of the mountain and analyze the elevation angle of the mountain top: set the peak position D, the projection E and DE=h at the bottom = H, then express AE, BE and CE respectively according to the elevation angles of the three points, and then establish an equation with cosine theorem to get H, so as to get the answer.
Solution: Let the top of the mountain be D, the bottom projection be E, and let DE=h, then AE=
three
h，BE=h，CE=
three
three
h
∫cos∠ABD+cos∠DBC = 0
∴
a2+(
2
h)2？ (2h)2
2a？
2
h
+
a2+(
2
three
three
h)2？ (
2
h)2
2a？
2
three
three
h
=0,
Solve h=
4 24
2
a.
So the answer is:
4 24
2
a
3. triangle, answer quickly. ad is the bisector
bae=eac
Because communication and iron are parallel.
So cae=fea
So fea=fae
It is easy to prove that fbe=feb
So fb=fe
So af=fb=fe
So af=bf
AB=AC, ∠ BAC = 120, D is the midpoint of BC, so the triangle abc is an isosceles triangle, so the three-point * * * line ad is. .. so abd=ade=30 Because triangle abd triangle ade is rt triangle, so AB = 2ad = 2ae, so ab=2ad=4ae, so be=ab-ae=3ae, so EB = 3ae.
4. jiangbei district 20 12 to 20 13 eighth grade math unit test questions1.3.1corner bisector eighth grade math final test questions (1) (test time: 90 minutes, full mark:/kloc-0. , multiple-choice questions (3 points * 10 =30 points) 1. If the upper base length of the trapezoid is 4 and the median length is 6, the lower base length of the trapezoid is () A.5 B.8 C. 12 D. 162. In statistics, the variance of the sample can approximately reflect the population () A. Average state B. Fluctuation size C. Distribution law D. Concentration trend 3. The significant digit of divisor-1.25* 10-3 is () A.3b.0c.6d.4. As shown in the right figure, in the square grid, B. Diagonal lines are equal and divided vertically. Diagonal lines are equally divided. D. Four sides are equal and four corners are equal. 6. It takes the same time for a ship to sail 90 kilometers downstream and 60 kilometers upstream. If the current speed is 2 kilometers per hour, find the speed of the ship in still water. If the speed of a ship in still water is x kilometers per hour, the equation can be listed as () A. B. C. +3= D. +3= 7. The two sides of Rt△ABC are 3 and 4 respectively. If the side length of a square is the third side of △ABC, then the area of this square is () A.25 B.7 C. 12 D.25 or 78. 1, m=, n=, then the relationship between m and n is () a.m >; The algebraic expression of nb.m = n c.ms2b.s 1 1): a = _ _ _ _ _ _ _ b = _ _ _ _ _ _, and c = _ _ _ _ _ _. (2) guess: a, B. and prove your guess. 2345…A 22- 1 32- 1 42- 1 52- 1…B 468 10…C 22+ 1 32+ 1 42+。 A school fumigates classrooms. It is known that the drug content per cubic meter of indoor air is directly proportional to the time x (minutes) when the drug burns, and inversely proportional to the time x (pictured) after the drug burns. Now it is measured that the drug burns for 8 minutes, at which time the drug content in the indoor air is 6 mg. Please answer the following questions according to the information provided: (65438+) The functional relationship between Y and X is _ _ _ _ _ _ _ _. (2) The research shows that students can enter the classroom only when the drug content per cubic meter in the air is lower than 1.6 mg, so it takes at least _ _ _ _ minutes to return to the classroom from the beginning of disinfection; (3) The research shows that only when the drug content per cubic meter is not less than 3 mg and the duration is not less than 10 minute can bacteria in the air be effectively killed. Is this disinfection effective? Why? 26.(6 points) As shown in the figure, in the known trapezoidal ABCD, AD∨BC, AB=DC, diagonal AC and BD intersect at point O, E is the moving point on the side of BC (point E does not coincide with points B and C), EF∨BD intersects with AC at point F, and EG∨AC and BD intersect at point G (. (2) Please change the condition of the above topic "In trapezoidal ABCD, AD∨BC, AB=DC" to another quadrilateral, and other conditions remain unchanged, so that the conclusion that "the perimeter of the quadrilateral EFOG is equal to 2OB" still holds, and draw the figure of the adapted topic, write out what is known, and verify it. It is not necessary to prove that a shopping mall sells a certain commodity .27, (6 points). * * * made a profit of 6000 yuan. In the second month, the mall held a promotion, and the purchase price of the goods increased by 10% as the sales price. The sales volume in the second month increased by 100 compared with the first month, and the mall made a profit of 2000 yuan more than the first month. What is the purchase price of this commodity? How many pieces did the mall sell in the second month? Mathematics final examination questions for the next semester of Grade 8 (3) (time 90 minutes, total score 100) Class name total score 1. Multiple choice questions (2 points for each question, ***24 points) (fill in the options in the table below)12345678910121. The results of the fifth national census show that the total population of China has reached 13000000. The correct result is a.1.3 *108b.1.3 *109c.0.13 *1010d. The result is a, b, c, d, 3. If the voltage across a constant resistor is 5 and the current flowing through it is 1, the approximate picture of the current flowing through this resistor changing with the voltage across it is (hint:) A B 4. If both x and y in the formula are enlarged by 2 times, the value of formula A is enlarged by 4 times; B, expand by 2 times; C, unchanged; D is reduced by 2 times. 5. As shown in figure 1, there is a right-angled triangular paper with two right-angled sides. Now fold the right-angled edge along a straight line so that it falls on the hypotenuse and coincides with it.
Vertices A, B, C and D in the rectangular ABCD are arranged clockwise. If in the plane rectangular coordinate system, the coordinates corresponding to point B and point D are (2,0) and (0,0) respectively, and point A and point C are symmetrical about X, then the coordinates corresponding to point C are (a) (1. - 1) (c) ( 1，-2) (d) (2，-2) 7。 In the following figures, the center is symmetrical but not axisymmetric (a) square (b) rectangle (c) rhombus (d) parallelogram 8, as shown in Figure 2. A quadrilateral ABCD should meet the following conditions: (a) one set of opposite sides is parallel, and the other set of opposite sides is not parallel; (b) The diagonal lines are equal; (c) Diagonal lines are perpendicular to each other; (d) The diagonal line is equally divided; 9. The following propositions are wrong: a. The diagonals of parallelograms are equal; B. The diagonal lines of the isosceles trapezoid are equal; C. Two parallelograms with equal diagonals are rectangles; D. The quadrilateral with vertical diagonal is rhombus 10. If the image of function y=2 x +k intersects with the positive semi-axis of Y axis, the quadrant where the image of function y= is located is A, the first, second, third and fourth quadrants are C, the second and fourth quadrants are D, and the first and third quadrants are 1 1. If it represents an integer, the integer A can have the value of A.65438+.