Let a = (1, sin θ), B = (COS θ, 1) A.B = - 3 / 5, then sin 2 θ=

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• 1. Let a (x1, Y1), B (X2, Y2) be functions f (x) = (1 / 2) + log2 (x / 1-x), and OM = (1 / 2) (OA + OB) The abscissa of point m is 1 / 2, and Sn = f (1 / N) + F (2 / N) + +F (n-1 / N), where n ∈ n * and N ≥ 2, (1) Calculate the ordinate value of point M; (2) Find S2, S3, S4 and Sn; (3) Given an = 1 / (Sn + 1) (Sn + 1 + 1), where n ∈ n *, and TN is the sum of the first n terms of the sequence {an}, if TN ≤ λ (Sn + 1 + 1) holds for all n ∈ n *, try to find the minimum positive integer value of λ
• 2. As shown in the figure, it is known that ray OC divides angle AOB into 1:3 parts and ray od divides angle AOB into 5:7 parts. If angle cod = 15 degrees, try to judge the position relationship between OA and ob
• 3. In the acute triangle ABC, if the angle a = 50 degrees and ab is greater than BC, the value range of angle B is in the range Wrong. AB and BC are sides
• 4. As shown in the figure, ∠ a = 52 ° o is the intersection of the vertical bisectors of AB and AC, then ∠ OCB=______ ．
• 5. In the triangle ABC, the angle a = 62 degrees, EO and fo are the vertical bisectors of AB and AC respectively and intersect at point O. calculate the degree of the angle BOC
• 6. In △ ABC, if O is the intersection of three bisectors and ab: BC: CA = 3:4:6, then the area ratio of △ AOB, △ BOC and △ COA is?
• 7. In 2004200520062007, the number that cannot be expressed as the square difference of two integers is?
• 8. It is known that the lengths of three sides of a triangle are three continuous natural numbers, and its circumference is 12cm. What are the lengths of three sides of the triangle? It's a formula!
• 9. If the three variable lengths of a triangle are known to be three continuous natural numbers and the maximum angle is obtuse, then the lengths of the three sides are
• 10. The sides of △ ABC are all integers, and the maximum side is 7. How many triangles are there?
• 11. Let vector OA = (3,1), vector ob = (- 1,2), vector OC ⊥ vector ob, vector BC parallel vector OA Then satisfy the vector od coordinates of vector od + vector OA = vector OC, (o is the origin)
• 12. Given that OA = ob = OC = a in tetrahedral o-abc, and the two are perpendicular, the radius r of the inscribed sphere of tetrahedral o-abc is calculated
• 13. If there is a point O in the plane of △ ABC, and OA * ob = ob * OC = OC * OA, then point O is the () center of △ ABC
• 14. As shown in the figure, it is known that the edges OA, OB and OC of o-abc are perpendicular, and OA = 1, OB = OC = 2, e is the midpoint of OC Find the sine value of the angle between the line be and the plane ABC. ② find the distance between the point E and the plane ABC
• 15. Given that points a (x1, Y1) and B (X2, Y2) are two moving points on the circle C1: (x-1) &# 178; + Y & # 178; = 4, O is the origin of coordinates and satisfies the vector OA * ob = 0, The circle whose diameter is ab is C2 (1) If the coordinate of point a is (3,0), find the coordinate of point B (2) Finding the trajectory equation of the center C2 (3) Finding the maximum area of circle C2
• 16. It is known that the values of formula 2A + 7 and 1-A are opposite to each other. Solve the equation 4-2a = 3x-1 about X
• 17. It is known that the solutions of the equations 4x + 2A = 3x + 1 and 3x + 2A = 6x + 1 are opposite to each other?
• 18. If the solution of the equation 9x-2 = KX + 7 of X is a natural number, then the value of integer k is______ ．
• 19. Let K be an integer and the solution of the equation KX = 6-2x about K be a natural number to find the value of K
• 20. 1-4 / 4 4-3x = 6 / 5x + 3-x process More complete