As shown in the figure, in the trapezoidal ABCD, ad ‖ BC, ∠ B = 90 °, ab = 14cm, ad = 18cm, BC = 21cm, point P starts from point a and moves 1cm / s along the ad edge to point D, and point Q starts from point C and moves 2cm / S along the CB edge to point B. if P and Q start from a and C at the same time, and the moving time is set to T seconds, then t=______ The trapezoid PQCD is an isosceles trapezoid

Let p be PN ⊥ BC in N, d be DM ⊥ BC in M, ∵ ad ∥ BC, ∵ B = 90 °, DM ⊥ BC, ∵ quadrilateral aBMD is rectangle, ad = BM. ∵ MC = bc-bm = BC-AD = 3. And ∵ QN = bn-bq = ap-bq = t - (21-2t) = 3t-21

RELATED INFORMATIONS

1. In the trapezoidal ABCD, ad is parallel to BC, ∠ a = 90 °, ad = 21cm, BC = 24cm, point e moves from point a to D at the speed of 1cm per second, and point F moves from point C to B at the speed of 2cm per second. If points E and f start from points a and C at the same time, how long do they move, the trapezoidal efcd is isosceles trapezoid?
2. As shown in the figure, in the quadrilateral ABCD, ∠ bad = ∠ BCD = 90 ° AB = ad, if the area of the quadrilateral ABCD is 24cm2, then the AC length is______ cm．
3. If the circumference of trapezoid ABCD is 25cm, ab \ \ CD, de \ \ BC and intersects AB with E, what is the circumference of triangle ade Can you give me more details? Maybe there are other ways?
4. In the trapezoid ABCD, ab | CD, the perimeter is 27, de | BC intersects AB at point E, CD = 4, what is the perimeter of the triangle ade
5. Known: as shown in the figure, in quadrilateral ABCD, angle DAB = 60 degrees, angle B = angle, ADC = 90 degrees, CD = 2, BC = 11, find the length of AC
6. As shown in the figure, in ladder ABCD, ad ‖ BC, be bisects ∠ ABC, and be ⊥ CD is the first moving point on be. If BC = 6, CE = 2DE, then the maximum value of | pc-pa | is______ ．
7. In the trapezoid ABCD, AB / / DC, CE are bisectors of angle BCD, and CE is perpendicular to ad, de = 2ae. CE divides the trapezoid into two parts: S1 and S2. If S1 = 1, s is obtained Sorry, there's no picture S1 is a quadrilateral abce, S2 is a triangle ECD
8. In a trapezoid ABCD, AB is parallel to CD, angle BCD equals 90 degrees, AB equals 1, BC equals 2, Tan angle ADC equals 2, and E is a point in the trapezoid The angle EDC is equal to the angle FBC and De is equal to BF. Try to judge the shape of triangle ECF and prove your conclusion
9. In trapezoid ABCD, ab ‖ CD, ∠ ABC = 90 °, ab = 5, BC = 10, Tan ∠ ADC = 2. (1) find the length of DC; (2) e is a point inside the trapezoid, f is a point outside the trapezoid, if BF = De, ∠ FBC = ∠ CDE, try to judge the shape of △ ECF, and explain the reason. (3) under the condition of (2), if be ⊥ EC, be: EC = 4:3, find the length of de
10. In trapezoidal ABCD, ad is parallel to BC, triangle ADC is 2:3 than triangle ABC, and the connecting line of diagonal midpoint m and N is 10 cm Finish it today as soon as possible
11. As shown in the figure, in the ladder ABCD, ad// BC.AB=CD The perimeter of trapezoid is 10cm, BC = 4cm, DB bisects ∠ ABC, try to find the length of AD,
12. As shown in the figure, in trapezoidal ABCD, ad ‖ BC, ad = 3, ab = 5, BC = 9, the vertical bisector of CD intersects BC at e and connects De, then the perimeter of quadrilateral abed is equal to () A. 17B. 18C. 19D. 20
13. As shown in the figure, in the trapezoidal ABCD, ad ‖ BC, ∠ bad = 90 ° and ∠ d = 45 °, EF is the vertical bisector of CD, and the perpendicular foot is e, The moving point t (m, n) represents the torch position, and the torch starts to pass from the m point 10 meters away from Beijing road The above explanation is wrong and should be correct As shown in the figure, in trapezoidal ABCD, ad ‖ BC, ∠ bad = 90 ° and ∠ d = 45 °, EF is the vertical bisector of CD, the perpendicular foot is e, EF intersects ad with m, and the extension line of Ba intersects F. Verification: BF = ad
14. In trapezoidal ABCD, AD / / BC, angle bad = 90 °, angle d = 45 °, EF is the middle perpendicular of CD, the perpendicular foot is e, Fe intersects ad at m, if ad = a, calculate BF value
15. It is known that in the isosceles trapezoid ABCD, ab = CD, ad is parallel to BC, point E is a point outside the trapezoid, and EA = ed Draw your own picture. Oh, Sheila!
16. In right angle trapezoid ABCD, BC ∥ ad ad ⊥ ad bottom ad = a oblique waist CD, the vertical EF intersects ad at g intersects Ba, and the extension line calculates BF length at f angle d = 45 °
17. As shown in the figure, it is known that in the rectangular trapezoid ABCD, BC ‖ ad, ab ⊥ ad, bottom ad = 6, the vertical bisector EF of oblique waist CD intersects ad at g, the extension line of intersection Ba intersects F, and ∠ d = 45 ° to find the length of BF
18. In the right angle trapezoid ABCD, BC ‖ ad, ab ⊥ ad, ∠ d = 45 °, the vertical bisector EF of oblique waist CD intersects ad at g, and the extension line of intersection Ba intersects F Practice question 17 on page 46 in eighth grade (next) class
19. 1. In the trapezoid ABCD, AD / / BC, ab = ad = DC = 2cm, angle c = 45 ° to find the perimeter of the trapezoid
20. (36 / 11 * 25.8-36 / 11 * 16076 + 18 / 55 * 19.6) * (1.25-7 / 12 + 5 / 36) Should be: （36/11*25.8-36/11*16.76+18/55*19.6)*(1.25-7/12+5/36）