It is known that 2x + y = 7 is a quadratic equation of X and y, and the solutions of the equations are positive integers

x. If y is all positive integers, then y must be odd. When y = 1, x = 3, when y = 3, x = 2, when y = 5, x = 1. Then the positive integer solution of this equation is x = 1, y = 5 or x = 2, y = 3 or x = 3, y = 1

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1. If we keep fixed points F1 (- 2,0) and F2 (2,0), then the locus of the moving point P satisfying the following conditions in the plane is hyperbolic A./PF1/-/PF2/=_ +3 B./PF1/-/PF2/=_ +4 C./PF1/-/PF2/=_ +5 D./PF1/^2-/PF2/^2=_ +4 Note: Pf1 / medium / is absolute value_ +3 is positive and negative
2. Simple calculation by factorization （1）22.4^2-27.6^2 （2）2.03*2.5+4.83*2.5+3.14*2.5 （3）1.25*14^2-125*8.6^2 （4）102^2-2*(100^2-2^2)+98^2 （5）27*1.8^2-12*1.2^2 （6）(1-1/2^2)(1-1/3^2)(1-1/4^2)…… (1-1/2008^2)
3. How many days are there from October 24, 2010 to today
4. The story about mathematics is less than 20 words! Within 100 words!
5. The level of air quality is related to the amount of pollutants in the air. What can be used to express it? If the pollution index is 101-200, the air quality is
6. Example (1) 8*73+52*8 =8*（73+52） =8*125 =1000 Example (2) 9*96+3+9 =9*（96=3+1） =9*100 =900 For my daughter's homework, I don't know how to calculate, why to calculate like this, and why, exercises 1、 54 * 99 + 99 + 45 II. 54 + 99 * 99 + 45 3、 100 * 89 + 89 * 11 + 89 * 89 IV. 100 * 89-89 * 11-89 * 89 There is also the question 5*999+5+99*7+7+4*9+4=
7. The simple calculation is (53.76-17.6) △ 1.8 (0.8 × 7 + 4.56 △ 1.9) × 12.5 15.73-（2.17+0.73）-1.83
8. The expression of parabola y = ax ^ 2 + BX through D (4,3) a (6,0)
9. If a divided by B equals 45, then (a multiplied by 3) divided by B equals (), and a divided by (b multiplied by 3) equals (). Thank you,
10. Calculation formula of trapezoid circumference Circumference!
11. Given that point a (0, - 1) and point B are moving points on the curve X ^ 2-y ^ 2 + X + 2Y + 3 = 0, then the trajectory equation of the midpoint of line AB is obtained
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13. 16 π of the angle is reduced to α + 2K π (K ∈ Z 0)
14. The form of - 1125 ° to 2K π + α (K ∈ Z, 0 ≤ α < 2 π) is () A. −6π−π4B. −6π+7π4C. −8π−π4D. −8π+7π4
15. The following angles are reduced to 0 to 2 π plus 2K π (K ∈ z) (1) -25/6π (2)-5π (3)-45° (4)400°
16. The - 1125 ° is reduced to 2K π + α (0 ≤ α < 2 π, K ∈ z)
17. The following angles are reduced to 2K π + a (0
18. The form of transforming - 1125 ° into α + 2K π (0 ≤ α & lt; 2 π, K ∈ z =) is ()
19. Change - 18 π / 7 to 2K π + α (0 ≤ α
20. -Square of a · (- a) · (- a) · (- a) · (- a) · (- a) · (- a) · 2K + 1