As shown in the figure, in the parallelogram ABCD, e is the midpoint of CD, connecting AE and extending, intersecting the extension line of BC at point F. if the area of the parallelogram is known to be 18, can you calculate the area of △ ABF

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• 1. It is known that in ▱ ABCD, if the areas of △ ade, △ bef and △ CDF are 5, 3 and 4 respectively, the area of △ def can be obtained
• 2. In the parallelogram ABCD, point E is on the edge AB, and point F is on the edge BC. The areas of △ ade, △ bef, and △ CDF are 5, 3, and 4 respectively. The area of △ CDE is calculated This is an exercise in the chapter "quadrilateral" in the eighth grade mathematics volume II of pep. Since you can't draw pictures here, please draw your own pictures according to the meaning of the title. It won't be difficult to draw Sorry, the problem should be to find the area of △ def.
• 3. In the parallelogram ABCD, the bisector BC of ∠ bad intersects at point E and the bisector DC intersects at point F (1) In Figure 1, it is proved that CE = CF; (2) If ∠ ABC = 90 ° and G is the midpoint of EF (as shown in Figure 2), write the degree of ∠ BDG directly; (3) If ∠ ABC = 120 ° FG ‖ CE, FG = CE, connect dB and DG respectively (as shown in Figure 3), and calculate the degree of ∠ BDG
• 4. It is known that, as shown in the figure, e and F are two points on the diagonal AC of the parallelogram ABCD, AE = CF
• 5. As shown in the figure, parallelogram ABCD, e, f are two points on AC, de ‖ BF, verification: AE = CF
• 6. It is known that, as shown in the figure, e and F are two points on the diagonal AC of the parallelogram ABCD, AE = CF
• 7. In the parallelogram ABCD, points E and F are points on AB and CD respectively, de / / BF
• 8. E. F is the two points on the diagonal AC of the parallelogram ABCD, de ⊥ AC, BF ⊥ AC, proof: the parallelogram debf is a parallelogram, urgent now!
• 9. The quadrilateral ABCD is a parallelogram, de ⊥ AC, BF ⊥ AC, and the perpendicular feet are e, F, be and DF respectively
• 10. As shown in the figure, in the angle ABCD, the points E and F are on AB and CD respectively, be = DF. It is proved that the quadrilateral debf is a parallelogram The graph is inside, and the line DB is removed
• 11. In the parallelogram ABCD, e is on DC, if de: EC = 1:2, then BF: be=______ ．
• 12. As shown in the figure, the quadrilateral ABCD is a parallelogram, be: EC = 1:2, f is the midpoint of DC, the area of triangle Abe is 12cm2, then the area of triangle ADF is______ cm2．
• 13. It is known that in a parallelogram ABCD, points E and F are on edges AB and BC respectively. (1) if AB = 10, the distance between AB and CD is 8, AE = EB, BF = FC, the area of △ DEF is calculated. (2) if the areas of △ ade, △ bef and △ CDF are 5, 3 and 4, the area of △ DEF is calculated
• 14. In the quadrilateral ABCD, ∠ B = ∠ d = 90 ° and AE and CF are bisectors of ∠ DAB and ∠ BCD, respectively It's a parallel CF...
• 15. As shown in the figure, in quadrilateral ABCD, angle B is equal to angle D is equal to 90 degrees, CF bisects angle BCD. If AE is parallel to CF, please determine whether AE bisects angle bad
• 16. In the arithmetic sequence {an}, A1 = 3, the sum of the first n terms is Sn, the items of the arithmetic sequence {BN} are all positive, B1 = 1, the common ratio is Q, and B2 + S2 = 12, q = s2b2. (1) find an and BN; (2) let the sequence {CN} satisfy the first n terms and TN of CN = 1sn, {CN}, and prove that TN < 23
• 17. In rectangular ABCD, points E and F are on line AB and ad respectively, AE = EB = AF = 2 / 3fd = 4. Along the straight line EF, the triangle AEF is folded into triangle a'ef, Make plane a'ef perpendicular to plane bef Finding a '- fd-c cosine of dihedral angle If the points m and N are on the line segments FD and BC respectively, and the quadrilateral mncd is folded upward along the line Mn, so that C and a 'coincide, the length of the line segment FM is calculated
• 18. Given square ABCD, de ratio EC = 3:2, EF vertical AE, then FC ratio EC = -, EF ratio AE = -, de ratio AE = -
• 19. In the square ABCD, the midpoint e of BC connects AE, and a point F on CD makes EF ⊥ AE connect AF. verify that AF = AD + FC
• 20. In square ABCD, point F is on ad, point E is on AB, AE = EB, AF = 1 / 4AD Connecting CE, EF (Pythagorean theorem, inverse theorem)