In trapezoidal ABCD, AD / / BC, median EF = 17cm, AC vertical BD, angle DBC = 30 degrees, calculate the length of diagonal AC

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• 3. If the tolerance of arithmetic sequence an is - 1 and a1 + A2 + a3 +... + A2008 = 5022, then A2 + A4 + A6 +... + A2008 =?
• 4. For integers a, B, C, D, the symbol ∣ A / D - B / C ∣ denotes the operation AC – BD. given that 1 ∣ 1 / D - B / 4 ∣ 3, what is the value of B + D?
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• 10. Xiao Ming, his father and his mother are playing on the seesaw. Their weight is 150kg. His father is sitting on one end of the seesaw. Xiao Ming, who weighs only half of his mother, is sitting on the other end of the seesaw with his mother. At this time, his father's end is still on the ground. Can you guess what range Xiao Ming's weight should be?
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• 12. The cross section of a section of Zhanghe reservoir dam is isosceles trapezoid, the width of dam crest is 6m, the width of dam bottom is 126m, the slope gradient is 1: root 3, then the slope angle and height of the dam here are?
• 13. The cross section of the reservoir dam is trapezoidal, the width of the dam crest is 5m, the slope ad = 6 √ 2m, the dam height is 6m, and the slope of the oblique wave bc i = 1: √ 3, Calculate the low width ab of the dam and the slope angle ∠ a of the slope ad
• 14. In the trapezoid ABCD, ad ‖ BC, angle a = 90 °, ab = 7, ad = 2, BC = 3, whether there is a point P on the straight line AB, and find out the length of AP In the trapezoidal ABCD, ad ‖ BC, ∠ a = 90 °, ab = 7, ad = 2, BC = 3, ask whether there is a point P on the line AB, so that the triangle with P, a, D as the vertex is similar to the triangle with P, B, C as the vertex? If not, please explain the reason; if so, how many p points are there? And calculate the length of AP
• 15. There are four digits ABCD, and ABCD = (AB + CD) square, find all such four digits
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• 17. In the triangle ABC, 1. If ∠ C = 90, cosa = 12 / 13, find the value of SINB. 2. If ∠ a = 35, B = 65, try to compare the size of cosa and SINB If this triangle is an arbitrary acute triangle, can we judge the size of cosa + CoSb + COSC and Sina + SINB + sinc There is no graph
• 18. It is known that: as shown in the figure, in trapezoidal ABCD, ad ‖ BC, BC = DC, CF bisects ∠ BCD, DF ‖ AB, and the extension line of BF intersects DC at point E
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