7Y + 7x = 21 solution process

Divide both sides by 7 at the same time, x + y = 3

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1. Solving equations and processes with x + 3,7x = 5,14
2. The solution equation is 0.8x-24 = 39.2
3. There are four numbers, of which the first three numbers form an equal ratio sequence, and the last three numbers form an equal difference sequence. The sum of the first and last two numbers is 14, and the sum of the middle two numbers is 12
4. As shown in the figure, e and F are the midpoint of line AC and ab respectively. If EF = 20cm, find the length of BC
5. How to distinguish stainless steel material, 201202304, what does it represent? Those will rust in the bathroom. 201202, will they rust in the bathroom?
6. (a + b) square, what is the square root
7. Merging congeners (7y-2x) - 7x-4y
8. How to solve 7x-4 × 3,5 = 24,5
9. X-1 / 8x-24 = 1 / 4x to solve the equation
10. Let four numbers, the first three of which are in turn equal ratio sequence, the last three of which are in turn equal difference sequence, and the sum of the first and last two terms is 14, and the sum of the middle two terms is 12
11. If the square root of a is ± 8, what is the cube of a?
12. The formula also needs to be improved Each side of an even die is marked with the number 123456, and the die is thrown once at will What is the probability that the number of points facing up is odd?
13. As shown in the figure, point C is a point on line AB, D and E are the midpoint of AC and BC respectively, then de = 0___ AB．
14. There are four numbers. The first three numbers form an equal difference sequence, and the last three numbers form an equal ratio sequence. The sum of the first and last two numbers is 7, and the sum of the middle two numbers is 6,
15. x-5/8x=36 (1+1/3)x=2/5 3/4x=5/7X14/35 x÷7/5=5/8÷1/3
16. When solving equation 7x-4 * 3.5 = 24.5, first calculate the product of () and then consider () as a whole
17. If X1 and X2 are the two real roots of the equation x ^ 2 - (2k + 1) x + K ^ 2 + 1 = 0, and X1 and X2 are greater than 1. If X1 / x2 = 0.5, find K
18. Given (A-7) square = 121, (B + 1) cube = - 0.064, find the square root of a + 10B
19. Roll a uniform regular hexahedron dice with 1, 2, 3, 4, 5 and 6 on each side. The probability of "5" or "6" is equal to () A. 13B. 14C. 15D. 16
20. As shown in the figure, D is the midpoint of AB, e is the midpoint of BC, be = 1 / 5, AC = 2cm, find the length of line De ·————·————·——·——· `A`````````D`````````B`````E````C