If x = 1 and 1 / 5 minus 9 / 20, y = 1 and 9 / 5 times 6 / 7, then are x and Y reciprocal

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• 1. Number reasoning 8,11,4,5,21,20,11 () Civil servants, why
• 2. What is the general formula of 1,1,2,3,4,5,6,7,8,9,10?
• 3. Three fifths of a number is nine fifths of a number. What's five sixths of a number?
• 4. Let the density function of random variable X be symmetric with respect to x = u, and prove that its distribution function satisfies the following requirements: F (U + x) + F (u-x) = 1 (x is between positive and negative infinity)
• 5. 2 / 7,3 / 11,1 / 3,7 / 19
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• 7. 5 out of 8 meters represents a fraction of 1 meter and a fraction of several meters
• 8. How many grams per square meter is an ounce per square yard
• 9. Number reasoning questions 1,3,4,6,11,19, ()
• 10. Any function f (x) defined on R can be expressed as the sum of an odd function g (x) and an even function H (x), X belongs to R, then, A,g（x）=x,h（x）=lg(10^x+10^-x+2) B,g(x)=1/2lg(10^x+1+x),h(x)=1/2lg(10^x+1+x) c,g(x)=1/2x,h(x)=lg(10^x+1)-x/2 D,g(x)=-1/2x,h(x)=lg(10^x+1)+x/2 Why not D
• 11. If all the vertices of a cuboid are on the same sphere and the lengths of the three edges on one vertex are 1, 2 and 3 respectively, the surface area of the cuboid is 0______ ．
• 12. In the parallelogram ABCD, we know AB = 10, root 3, B = 60 ° and AC = 30, then we can find the area of the parallelogram Speed, speed! Thank you! ~
• 13. There are four points P, a, B, C on the sphere, PA, Pb, PC are perpendicular, PA = 3, Pb = 4, PC = 5, so how to calculate the sphere area?
• 14. As shown in the figure, there are four points P, a, B and C on the sphere. If PA, Pb and PC are perpendicular to each other, and PA = Pb = PC = a, the surface area of the sphere is______ ．
• 15. As shown in the figure, there are four points P, a, B and C on the sphere. If PA, Pb and PC are perpendicular to each other, and PA = Pb = PC = a, the surface area of the sphere is______ ．
• 16. Let P, a, B and C be the four points on the surface of ball o, PA, Pb and PC are perpendicular, and PA = Pb = PC = 1, then the surface area of ball o is______ ．
• 17. On the mathematical problems of Liberal Arts in senior high school about the proof of plane geometry If a vertex B and C that circle △ ABC, and give AB and AC to point D and point e respectively, the problem of AD: AC = AE: AB is not given graphics... I'm liberal arts, so don't use science knowledge to solve it... Otherwise I can't understand it... Thank you!
• 18. In the right triangle ABC, the angle ACB is equal to 90 degrees, CD is perpendicular to AB, and the perpendicular foot is d. let BC be equal to a, AC be equal to B, AB be equal to C, CD be equal to H
• 19. In the triangular prism ABC = a1b1c1, ab = Aa1 and cab = 90 degrees 1) It is proved that CB1 is perpendicular to BA1 (2) Given AB = root 2, BC = heel 5, find the volume of the triangular pyramid c1-aba1
• 20. If the side of a regular triangular pyramid is a right triangle and the side length of its bottom is a, then the side area of the pyramid is. Please attach a picture