Some problems in the second chapter of Physics What unit of physical quantity is "light year"? How many kilometers is the distance between Altair and vega? Why is it often called "astronomical number" when describing a large number?

It's like a triangle. If you know the length of both sides and the angle between them, you can calculate the third side, that is, the distance between Taurus and Vega. Taurus is 16 light-years away from the earth and Vega is 27 light-years away

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1. As shown in the figure, the side length of square ABCD is 2, point E is the midpoint of BC side, BG ⊥ AE is made through point B, the perpendicular foot is g, extend BG to intersect AC at point F, then CF=______ ．
2. The period of sine function y = SiNx is () the maximum value is () the minimum value ()
3. Divide a circle into several parts evenly and form an approximate rectangle. The perimeter of the rectangle is 8 cm longer than that of the circle. What is the area of the circle______ Square centimeter
4. Given xn = [1 + (- 1) ^ n] / n how to prove his limit is 0 by definition
5. The perimeter of a square steel plate is 8 / 15 meters, and its area is square meters
6. Let x1, X2 If xn is a sample from the population x ~ n (0,1), then the mathematical expectation of the sample mean is?
7. The floor area of the room is 14.4 m2, and the floor is laid with exactly 40 identical square tiles. What is the side length of each tile? The accuracy of the results was 0.01
8. Calculation integral ∫ 1 / (x * LNX) DX
9. My mother is going to buy a square tablecloth for the round table at home. The diameter of the round table is 1.3 meters and the height is 1.5 meters My mother is going to buy a square tablecloth for the round table at home. The diameter of the round tablecloth is 1.3 meters and the height is 1.5 meters. If you want to make the square tablecloth just touch the ground, how many meters should the diagonal length of the square tablecloth be? Have a formula!
10. Given that FX is an even function of period 2 and an increasing function in the interval [0,1], then f (- 5.5), f (- 1) and f (0) are of the same magnitude
11. Cut a rectangle 2cm wide from the square iron sheet, and the remaining area is 35cm2, then the original area of the iron sheet is 35cm2
12. The sixth grade mathematics application question and according to the process row synthesis formula Start - with 1 / 5 + 3 / 7 - subtract the previous sum with 1 - remove the previous difference with 1 / 4 - stop Start - half - quarter - subtract the sum from 3 - multiply the difference by one sixth - stop Department stores planned to sell 5 million yuan last year. In fact, they completed three fifths of the sales plan in the first half of the year and five eighths of the plan in the second half of the year. How many million yuan more than the plan last year?
13. Known circle area is 452.16 square meters, radius, diameter, perimeter!
14. A mathematical problem Some fresh vegetables are transported from the market, among which radish accounts for one fifth of the vegetables and green vegetables account for 35% of the vegetables. It is known that green vegetables are 450 kg more than radish. How many kg are there in total? The answer is 3000 kg!
15. In the parallelogram ABCD, BC = 6cm, s parallelogram ABCD = 28, then the distance between AD and BC is?
16. If it costs about 4 tiles for 5 square meters, and each tile costs 4.8 yuan, how much does it cost to buy a tile of 1 square meter?
17. The space quadrilateral ABCD is cut by a plane, e, F, G and H are respectively on AC, CB, BD and DA, and the section efgh is rectangular
18. Xiaoming's dining table is round. Mother wants to match the dining table with a square tablecloth. The diameter of the table is 1.5 meters and the table is high 1.2 meters, to make a square tablecloth
19. Mom is going to buy a square tablecloth for the round table at home. The diameter of the round table is 1.2 meters, and the height of the table is 0.9 meters. If you want to make the four corners of the square tablecloth on the table just touch the ground, how long should the diagonal of the square tablecloth be?
20. My mother is going to buy a square tablecloth for the round table. The diameter of the round table is 1.4 meters. If the four corners of the square tablecloth are just under the table Drop 40 cm, mother needs to buy how large a square tablecloth?