Summation difference product formula and summation difference formula

The integral sum difference formula: sin α sin β = - [cos (α + β) - cos (α - β)] / 2cos α cos β = [cos (α + β) + cos (α - β)] / 2Sin α cos β = [sin (α + β) + sin (α - β)] / 2cos α sin β = [sin (α + β) - sin (α - β)] / 2 and the differential product formula: sin θ + sin φ = 2Sin [(θ + φ) / 2]

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1. The result can be 48 by filling in the operation symbol between every two of the 10 natural numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10?
2. Sum difference product formula,
3. 1 2 3 4 5 = 200 add operation symbol
4. Equal product and equal difference sum formula!
5. How to add the operation symbol 1 2 3 4 5 6 = 5
6. An satisfies A1A2 = 1 / 3, A3 = 1 / 9, find the general term formula
7. Add a plus or minus sign before 2 3 4 5 6 7 8 9 to make the number equal to ten
8. 1,0,0,1,1,0,0…… The general term formula of It's best to use the method I know. I'm a freshman in senior high school and only know trigonometric function
9. Here you are: 1.2.3.4.5.6.7.8.9?
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11. How to calculate the results of five five, using + - * / four operation symbols each time, which are equal to 2,3,4,6 respectively
12. The function f (x) = ax ^ 2 + 2 (A-3) + 1 is a decreasing function in the interval (- 2, + ∞). Find the value range of real number a!
13. The square of x minus 10x plus 25 equals 0. How much does x equal?
14. Whose domain of definition is required in y = LG (x2 + ax + 2), X or the whole formula of x2 + ax + 2
15. The algorithm of the answer to a probability question is C14 (4 below) * C16 (6 below) / c210 (10 below) = 5 / 18?
16. The square of x plus 10x plus 16 equals 0
17. We can't separate the possible events from the possible events, Haizhou Haina company must pack five first-class products into a box when exporting a kind of parts. A worker mistakenly put two first-class products into a box when operating. Now he must inspect the second-class products and reload them into the first-class products. 1 if two first-class products are sampled each time, write down all the basic events 2 take two pieces at a time and find the probability of at least one second-class product (1) Two first-class products, one first-class product, one second-class product, two second-class products (2) C (2,1) C (3,1) + C (2,2)} / C (5,2) = 7 / 10, which means that it is possible to take one and another from two equal, and then add the possibility of taking all two equal, and divide by the total number of two equal. That's the probability of this problem, right? But why is it an equal possible event But the probability is 2 / 3, isn't it? Pick out two pieces that are either second-class or first-class Why not wait for a possible event
18. The square of X is 9. How much is x?
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