Calculation: (- 2000 5 / 6) + (- 1999 2 / 3) - (4000 3 / 4) - (+ 1 1 / 2)

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• 1. In the observation chart of the problem solution of "innovation class refining" in grade one of junior high school, the numbers corresponding to the four points of ABCD on the number axis are all integers, and their corresponding numbers are ABCD, and C-2A = 7 —.—.—.—.—.—.—.—.—.—.—> A B C D Then the origin should be a or B or C or
• 2. The fourth power of 9x - the square of 6x + 1-A power B power factorization
• 3. For two-phase 380V electric welding machine, it is said that the voltage difference between two phases is 380V when connecting two phases, but the control circuit is 220V. How can it also connect two phases?
• 4. 3m(m+1)^2=?
• 5. As the resistance increases, the power consumption will decrease 1. Getting bigger 2, smaller 3. Unchanged 4. Unable to judge
• 6. On several mathematical problems of fractions (1) The distance between station a and station B is 1280km. After adopting the "harmony" EMU to increase the speed, the running speed of the train is 3.2 times of the original, and the time from station a to station B is shortened by 11 hours, so the speed of the train after increasing the speed can be calculated (2) The distance between a and B is 36km. A and B start from a and B at the same time and walk towards each other. When they meet, a is 16km away from B. after meeting, they continue to move forward. A arrives at B 1.8h earlier than B arrives at a. find out the walking speed of a and B
• 7. The power loss of the conductor is 20% of the transmission power when the voltage of 220 V is used in a substation. If the power loss of the conductor is to be reduced to 5% of the transmission power, what is the transmission voltage?
• 8. Solution: to make the image of function y = (2m-3) x + (3m + 1) pass through the positive half axis of X and Y axis, what is the value range of M?
• 9. A resistor with a resistance value of 6 ohm, in a period of time, the amount of electricity passing through it is 2 banks, and the heat generated by the resistor is 12 joules______ V, it's been a long time______ Seconds
• 10. What is the fourth digit to the left of the decimal point in the decimal? What is its counting unit?
• 11. M is the middle point of BC side in triangle ABC, DM is vertical to em, D and E are on AB and AC respectively, connecting De, proving that De is less than BD = CE
• 12. 16x2y-16x3-4xy2．
• 13. If sample X1 + 2, X2 + 2 If the average of XN + 2 is 10 and the variance is 3, then the sample 2x1 + 3, 2x2 + 3 The average value of 2xn + 3 is (), and the variance is (), standard deviation Can you write more clearly? I read a lot of similar answers, but I can't understand them Well, I admit that I'm not good at understanding
• 14. How many natural numbers from 1 to 1998 are squared by 72?
• 15. When linear algebra asks what value a takes, the following vector groups are linearly related? A1 = (a, 1,1) ^ t, A2 = (1, a, - 1) ^ t, A3 = (1, - 1, a) ^ t (need the whole process, thank you
• 16. 9.2 - (3.6 + x) = 1.6
• 17. In the rectangular coordinate system, O is the origin, a (3,1), rotate point a 90 ° counterclockwise around o to point B, then the coordinate of point B is______ ．
• 18. 21 vs () = 18
• 19. The infinite discontinuity of function f (x) = X-1 / x ^ 2-1 is?
• 20. If a and B are real numbers and (5a + 6) square + lb-3l = 0, find the value of a / b