How many 5-digit combinations are there for any five digits (not repeated) from 0 to 9? It's better to attach the formula,

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• 1. The line L with slope 2 intersects with hyperbola (x ^ 2) / 3 - (y ^ 2) / 2 = 1 at two points a and B, and the absolute value of AB is 4. The equation of line L is obtained y=2x+b. x²/3-（2x+b)²/2=1. 10x²+12bx+3b²+6＝0. |x1-x2|＝√（24b²-240）／10. |y1-y2|＝2√（24b²-240）／10. （x1-x2）²＋（y1-y2）²＝16. b²＝55／3.b＝±√165／3. The linear equation is: L1: y = 2x + √ 165 / 3 L2:y＝2x-√165／3. |x1-x2|＝√（24b²-240）／10. |y1-y2|＝2√（24b²-240）／10. This step is not clear! √（24b²-240）／10. How did it come about
• 2. Please solve the math problem. Thank you for using the method of adding and subtracting fractions! 1. The original apple, pear, banana three kinds of fruit each 40 kg, now the apple left its 1 / 2, pear left its 2 / 5, banana sold its 3 / 4, which fruit left the most? 2. Xiaohua read a story book. He read 2 / 15 of the whole book on the first day, 3 / 20 of the whole book on the second day, and the sum of the previous two days on the third day. How much is left? Is there an answer? Oh, please
• 3. On the root of quadratic equation AX2 + BX + C = 0 Can't you be sure
• 4. If it is a rational number and │ a = - A, then a is negative or zero, Choose from the following: A. positive B. negative C. positive and zero D. negative or zero
• 5. The equations - 5x & # 178; + 1 = 6x, and (x + 1) &# 178; = 2x are reduced to general expressions
• 6. Fractional multiplication and division 1. How many air conditioners are sold in the first day, one-third of them in the second day, 14 in the third day? 2. A pile of goods is transported 4 / 15 of the first time, and the second time is 2 tons more than the first time. How many tons are there? What is the probability and usage of unit "1"? Find out how to use unit 1? How to find it?
• 7. Higher integral problem 1 / Sint DT thank you
• 8. How to solve the math problems of grade four without equations? Xiao Ming's father is 27 years older than Xiao Ming. Four years later, his father's age is four times that of Xiao Ming. How old is his father now?
• 9. P is the point on the ellipse x ^ 2 / 25 + y ^ 2 / 16 = 1, F1 and F2 are the left and right focal points, and the angle f1pf2 = 60 °, then what is the area of △ pf1f2
• 10. Solving simple mathematical problems in volume one of grade five
• 11. If the solution of the equations 3x + 2Y = m + 14x + 3Y = m − 1 satisfies x > y, then the value range of M is () A. m＞-6B. m＜6C. m＜-6D. m＞6
• 12. It's negative addition and subtraction, The meteorological observation data of the sounding balloon in a certain place show that the air temperature will decrease by about 6 ℃ for every 1 km increase in height. If the ground temperature is 21 ℃ and the temperature is minus 36 ℃ in the upper air, what is the height of this place? The meteorological observation data of a sounding balloon in a certain place show that the temperature will decrease by about 6 ℃ for every 1 km increase in altitude. If the ground temperature is 21 ℃ and the temperature at a place in the upper air is minus 39 ℃, how many kilometers is the altitude here
• 13. If point P [x, y], XY is less than 0 and X + y is greater than 0, then the position of point P in the coordinate plane
• 14. Given that the point (1,1 / 3) is a point on the image of the function f (x) = a ^ x (a > 0 and a ≠ 1), the sum of the first n terms of the proportional sequence {an} is f (n) - C, the first term of the sequence {BN} (BN > 0) is C, and the first n terms and Sn satisfy sn-sn-1 = √ Sn + √ sn-1 (n ≥ 2) 1) Finding the general term formula of sequence {an} and {BN} 2) If the sum of the first n terms of the sequence {1 / bnbn + 1} is TN, what is the minimum positive integer n with TN > 1000 / 2009 From the meaning of the title 1）a=1/3,an=fn-c-（f（n-1）-c） =fn-f（n-1） =-How to launch 2 / 3 * (1 / 3) ^ (n-1)? ∴Tn=1/2（1-1/2n+1)=n/2n+1＞1000/2009 The solution is n > 1000 / 9 The minimum value of n is 112
• 15. Given that the point (1,1 / 3) is a point on the image of the function f (x) = a ^ x (a > 0 and a ≠ 1), the sum of the first n terms of the proportional sequence {an} is f (n) - C, and the sequence {BN} Given that the point (1,1 / 3) is a point on the function f (x) = a ^ X image, the sum of the first n terms of the proportional sequence an is f (x) - C, and the first term of the sequence BN is C, and the first n terms and Sn satisfy SN-S (n-1) = √ Sn √ s (n-1): ① the general term formula of the sequence an and BN; ② If the sum of the first n terms of the sequence {1 / BN * B (n 1)} is TN, ask TN From the meaning of the title 1）a=1/3,an=fn-c-（f（n-1）-c）=fn-f（n-1）=-2/3*（1／3） ^（n-1） The sum of the first n terms of an is (1 / 3) ^ n - 1 ∴c=1 And ∵ SN-S (n-1) = √ Sn + √ s (n-1) ∴√Sn-√Sn-1=1 ∴√Sn=n,Sn=n^2 ∴bn=Sn-Sn-1=2n-1 2) BN is substituted into 1 / bnbn BN + 1 = 1 / (2n-1) (2n + 1) = 1 / 2 (1 / 2n-1-1 / 2n + 1) ∴Tn=1/2（1-1/2n+1)=n/2n+1＞1000/2009 The solution is n > 1000 / 9 The minimum value of n is 112 ∴√Sn-√Sn-1=1 ∴√Sn=n,Sn=n^2 How is Sn = n deduced?
• 16. Is the cubic power of 3AB the same as the cubic power of 2A? Why? After answering the above questions,
• 17. If the m-th power of 3a and the 2-th power of B are similar to the n-th power of 2 / 3AB, then the sum of the two terms is ()
• 18. 5 (the third power of a) 4-13 (the sixth power of a) 2
• 19. How to add 2 to the 100th power of 2 plus 2 to the 99th power of 2 plus 2 to the 98th power of 2
• 20. The square of two and a quarter times the square of four is calculated by a simple method