Pentagram is an axisymmetric figure. How many axes does it have?

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• 1. A circle is an axisymmetric figure. There are countless axes of symmetry, and its axis of symmetry is the diameter of the circle?
• 2. It is known that a is the unit vector in the plane. If B satisfies b * (a-b) = 0, then the value range of the module of B is? Why not - 1 ≤| B | ≤ 1
• 3. As shown in the figure, △ ABC, D and E are the midpoint of BC and AC respectively. BF bisects ∠ ABC and intersects de at point F. if BC = 6, the length of DF is______ ．
• 4. How to find the cosine of the angle between two vectors!
• 5. As shown in the figure, ab ∥ CD, ∠ ACB = 90 °, e is the midpoint of AB, CE = CD, de and AC intersect at point F
• 6. What is the multiplication of two vectors with equal modules and opposite directions
• 7. As shown in the figure, in the triangle ABC, high AD and be intersect at h, AC = BH
• 8. Given the vector a = (- 1,1), B = (4,3), how to find their scalar product?
• 9. The triangle is a trigonometric arithmetic sequence with the circumference of 36 and the circumference of the inscribed circle of 6 π Calculate a side length of 12, inscribed circle radius of 3, then how to do
• 10. Let a > 0, b > O, prove: ln (a + b) / 2 > = (LNA + LNB) / 2
• 11. One yuan equation application problem (sixth grade) SOS! It's 30 kilometers per hour from home to the railway station, 15 minutes earlier than the train's departure time. If it's 18 kilometers per hour, it's 15 minutes later than the train's departure time?
• 12. On a 1:500 scale plan, the perimeter of a rectangular classroom is 10cm, and the ratio of length to width is 3:2 Find the ratio of the area on the picture to the actual area of the classroom Write the ratio of area to time area on the graph and compare it with the scale. What do you find?
• 13. Eighth grade mathematics volume I mid-term test questions which have
• 14. The story of curved moon, stars and round moon
• 15. Using vector to solve four centers of triangle Note: generally, capital letters represent vectors, and vector * vector represents the product of two vectors 1. Prove that point O is the center of gravity of triangle ABC, which is AOB = BOC = COA 2. Prove: if h is a point in the plane of triangle ABC, and the square of the module of HA + the square of the module of BC = the square of the module of HB + the square of the module of Ca = the square of the module of HC + the square of the module of ab, then h is the perpendicular center of triangle ABC 3. Prove: if OA * (module of AB / AB - module of AC / AC) = ob * (module of Ba / BA - module of BC / BC) = OCT (module of Ca / Ca - module of CB / CB) = 0, then o is the inner core of triangle ABC 4. Prove that point O is a certain point on the plane, A.B.C is three non collinear points on the plane, the moving point P satisfies OP = OA + m (cosine value of the module and angle B of AB / AB + cosine value of the module and angle c of AC / AC), and M is greater than 0, then the trajectory of point P must pass the perpendicular center of triangle ABC
• 16. The bottom of a right angled trapezoid is 1.5 times of the top, and the top is extended by 16 cm to become a square. The area of the right angled trapezoid is calculated Elementary school mathematics, not equations
• 17. In tetrahedral a-bcd, e and F are the midpoint of edges AD and BC respectively, connecting AF and CE, (2) Sine value of the angle between CE and BCD. (PS:)
• 18. In the figure shown in the figure, all quadrangles are squares, all triangles are right triangles, and the maximum square surname side length is 7 cm Find the area sum of a.b.c.d
• 19. Given the function y = (A-X) / (x-a-1), the center of symmetry of the image is (3, - 1), then the real number a is equal to
• 20. There are 61 pieces placed in several squares, each of which must be placed. A maximum of 5 pieces can be placed in one lattice. At least how many squares have the same number of pieces?