As shown in the figure, when the triangle ABC paper is folded along De, and point a falls inside the quadrilateral BCDE, the quantitative relationship between ∠ A and ∠ 1 + 2 is

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• 1. As shown in the figure, fold the paper △ ABC along De, point a falls at a ′, ∠ 1 + ∠ 2 = 150 °, then ∠ a=______ ．
• 2. As shown in the figure, fold the triangle paper ABC along de. when point a falls on the inner A1 of the quadrilateral BCDE, if ∠ 1 = 50 °∠ 2 = 20 °, calculate the degree of ∠ A1
• 3. As shown in the figure, fold the paper triangle ABC along de. when point a falls inside the quadrilateral BCDE, what is the relationship between angle A and angle 1 plus angle 2? Explain the reason
• 4. As shown in the figure, fold the triangle ABC paper along De, when point a falls inside the quadrilateral BCDE, ∠ a, ∠ 1, ∠ 2 When point a falls in the interior of the quadrilateral BCDE, what is the quantitative relationship among the degrees of ﹥ a, ﹥ 1, ﹥ 2? Please write it down and explain why
• 5. As shown in Figure 8, fold triangle ABC along De, when point a falls inside the quadrilateral BCDE As shown in the figure, when the triangle paper ABC is folded along De, when point a falls inside the quadrilateral BCDE, there is a quantitative relationship between a and ∠ 1 ＋ 2, which always remains unchanged. Please find out this rule? And write down the reasons
• 6. In the acute triangle ABC, ah is high, if AB + BH = HC, prove: angle B = 2, angle c (to process,) In the acute triangle ABC, ah is high, if AB + BH = HC, prove: angle B = 2, angle C
• 7. In triangle ABC, CD is the angular bisector, CF is the outer angular bisector, DF is parallel, BC intersects AC and E, CF intersects F, and de = EF is proved
• 8. It is known that the area of triangle ABC is 42.3 square centimeters, which is six times of the area of triangle EFB, and the area of parallelogram efcd
• 9. As shown in the figure, in RT △ D is the midpoint of the hypotenuse AB, f is the midpoint of AC, EF ‖ DC, intersects the extension line of BC at point E, and proves that the quadrilateral befd is isosceles trapezoid
• 10. It is known that in RT triangle ABC, D is the midpoint of hypotenuse AB, de / / BC, EF / / DC
• 11. As shown in the figure, ABC, AB are equal to 10 cm, BC is equal to 7 cm, AC is equal to 6 cm. Fold the triangle along the straight line passing through point B so that point C falls at point E on the edge of AB, and the crease is BD. calculate the perimeter of the triangle AED
• 12. As shown in the figure, the triangle paper ABC, ab = 10cm, BC = 7cm, AC = 6cm, fold the triangle along the straight line passing through point B, so that the vertex C falls at point E on the edge of AB, and the crease is BD, then the perimeter of △ AED is______ cm．
• 13. As shown in the figure, D is a point on the edge AC of △ ABC, ed parallel BC intersects AB at point E, DF parallel AB intersects BC at point F, AE = one third AB, if the area of △ AED is 2, calculate the area of △ DFC
• 14. To seek for the combination of 1998 + 1999 + 2000 + 2001 +. + 2006 + 2007 + 2008
• 15. X-4x + 2Y + 2Y + 9 / 2 = 0, find XY
• 16. How much is 4x ^ 2Y · (- XY ^ 2) / x ^ 2Y ^ 4? It's better to have a process. Thank you~~ How much is (3x + 2) (x-3) - 3 (X-2) ^ 2?
• 17. Junior high school mathematics known (4x-2y-1) + root XY-2 = 0, find the value of 4x ^ 2y-4x ^ 2Y ^ 2 + XY ^ 2
• 18. Factorization 3x ^ 4 + x ^ 2y-2y ^ 2
• 19. Factorization (1) 3x (a-b) - 2Y (B-A); & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; (2) 4x2-9y2
• 20. 3x（a-b）+2y（b-a）