As shown in the figure, the line AB = 4, C is a moving point on the line AB, with AC and BC as sides, the equilateral triangle ACD and equilateral triangle BCE are made, Finding the minimum value of de

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• 1. Point C is an arbitrary point on the line AB, with AC and BC as sides respectively as regular triangles. Note that the area of △ BCE is S1, and the area of △ ACD is S2 If C is the golden section of AB and AC > BC, S1: S2 is obtained
• 2. As shown in the figure, ab ∥ CD, ∠ ACB = 90 °, e is the midpoint of AB, CE = CD, de and AC intersect at F.; De is perpendicular to AC, and angle ACD = angle As shown in the figure, it is known that AB / / CD, ∠ ACB = 90 °, e is the midpoint of AB, CE = CD, de and AC intersect at F, and the verification is as follows:
• 3. When the bulb is always marked with "220 V 40 W", the current passing through the filament is - A, one degree of electric energy for the lamp to work normally for - hours There must be a way to solve the problem!
• 4. AC power problem The maximum value of alternating current (sine cosine type) is 250 root 2 v. if a fuse is connected, the maximum current allowed by the fuse is 10a, and the maximum output power allowed is 5000W. What's wrong? The voltage is 250 bar No. 2, and the fuse is the effective value, so the maximum current is 10 bar No. 2, and the maximum power is 250 bar No. 2 * 10 bar No. 2 = 5000?
• 5. What is a ton represented by a symbol
• 6. Conversion of capacitance units? Capacitance units include h, uh, pH, etc. What's the conversion between them? It seems that there is any relationship between MH and NH?
• 7. Function y = 2-2x what is the square unit of the area of the triangle formed by the image and two coordinate axes
• 8. 1、 Fill in (15 pieces) 1. The sun is the largest () and () on earth 2. Light is transmitted in the form of (). The speed of light propagation is very fast, about () thousand kilometers per second. The distance between the sun and the earth is about 150 million kilometers, and it takes () minutes for the light from the sun to reach the earth 3. In the food chain, the organisms that can make their own food are called (). The organisms that consume the food made by other organisms directly or indirectly are called (). The food chain usually starts from () and ends at () 4. Seed germination needs (), suitable (), and sufficient () 5. An object like an electric light that can emit light on its own is called () 6. We found that earthworms like to live in (), () environment 2、 Judgment (10) 1. In order to observe the light source, Xiao Ming often looks directly at the light source with his eyes 2. The amount of light has nothing to do with the intensity and temperature 3. Seeds will not germinate in dark environment 4. In order to study whether the seeds germinate fast under the condition of moderate water or little water, the water content of the seeds in the experimental group and the control group are different, and the conditions of temperature, nutrient, air and light are also different 5. In the experiment of mung bean seed germination, the number of seeds in each group should be at least two 6. Solar energy is a kind of clean, safe and energy-saving energy. People are vigorously developing and using solar energy 7. If one kind of living thing is extinct, it will affect the survival of many other living things. Therefore, to protect one kind of living thing is to protect many living things 8. All the light sources are heating when they are emitting light 9. While the sun brings us light, it also brings us warmth 10. The transmission route of sunlight cannot be changed 3、 Multiple choice questions (10) 1. The doctor brought a frontal mirror to examine the patient's ears, which solved the problem by using () A. Direct light B, reflection of light 2. In contrast experiments, we generally control () condition unchanged A one B two C three 3. Apple trees are not suitable to be planted in tropical areas, and oranges are not suitable to be planted in the north A. Sunshine B, temperature C, water D, air 4. Space suits are usually made of silver for () A. Absorb solar energy B. prevent radiation C. beautiful 5. Fish must live in the water. Once they leave the water, they will die. This is because () A. Organisms affect the environment B. organisms change the environment C. organisms depend on the environment 4、 Various mirrors are used in many places of life and production, and the following types of mirrors are connected The doctor's frontal mirror Concave mirror of automobile Periscope plane mirror Convex lens of spherical mirror at road corner Solar cooker 5、 Short answer: 1. Use the animals given below to write three food chains: snake, frog, locust, bird, vole, rice and owl (6) 2. Please design and make a simple solar water heater. (requirements: write down the materials and simple steps or draw a simple diagram) (4 pieces)
• 9. Let an be an arithmetic sequence with nonzero tolerance, Sn be the sum of the first n terms of an, and S3 ^ 2 = 9s2, S4 = 4s2, The formula of finding sequence an
• 10. Kobayashi and Kobayashi are both stamp collectors. Kobayashi collected 72 stamps. The ratio of Kobayashi to Kobayashi is 4:3 To know how many stamps Xiao Gang collected, how many ways can you answer them
• 11. C is a point on the line AB, with AC and BC as edges, make equilateral △ ACD and equilateral △ BCE on the same side of AB, AE and CD intersect at m, BD and CE intersect at n It is proved that (1) △ MCN is an equilateral triangle. (2) if AC: CB = 2:1, then de ⊥ CE
• 12. Given that the point C is any point on the line AB (C does not coincide with a or b), AC and BC are taken as sides respectively, and the equilateral triangle ACD and equilateral △ BCE, AE and C are made on the same side of ab D intersects with m, BD intersects with CE with n The results show that: (1) ace ≌ DCB; (2) ACM ≌ DCN; (3) Mn ∥ ab
• 13. As shown in the figure, BD is divided into two parts, be is divided into ABC 2:5, DBE = 21 ° and the degree of ABC is calculated
• 14. As shown in the figure, BD is divided into two parts, be is divided into ABC 2:5, DBE = 21 ° and the degree of ABC is calculated
• 15. As shown in the figure, BD is divided into two parts, be is divided into ABC 2:5, DBE = 21 ° and the degree of ABC is calculated
• 16. As shown in the figure, make equilateral triangles △ abd, △ EBC, △ fac on the same side of BC with the three sides of △ ABC respectively, and prove that the quadrilateral ADEF is a parallelogram
• 17. As shown in the figure, D is a point on side AC of triangle ABC, CD = 2ad, AE is perpendicular to BC and E, if BD = 8, Tan angle abd = 3 / 4, find the length of AC
• 18. In triangle ABC, ad is perpendicular to BC and D, be is the middle line, and the angle EBC is 30 degrees
• 19. As shown in the figure, ad and be are the heights of BC and AC respectively in ABC
• 20. As shown in the figure △ ABC, ∠ BAC = 90 & ordm;, ad ⊥ BC, ∠ Abe = ∠ EBC, EF ⊥ BC, FM ⊥ AC, DF = FM