1. Flexible choice of parallel line method of determination to prove it; (focus) 2. Determination of the application of parallel lines in real life ... (hard point) i. The situation is as graphed. Refurbishers are nailing wooden bars to the wall. If the wood barb is vertically to the edge of the wall, how much degree does a wood bara parallel to a wood barb? To solve this problem, we need to find out the parallel determinations. For example, the following four conditions are present: 1 ∠b+ ∠bcd = 180°; 2 ∠1 = ∠2; 3 ∠3 = ∠4; 4 ∠b = ∠5 which determines that the conditions of a∥cd are () a. 1 b. 2 c. 3 d. 4 based on the determining theorem of the parallel line, an answer can be obtained. 1 ∵∠b +bcd = 180°, °ab ∥c; 2 ∵∠b ∥c; 3 ∵∠b =4 ∠ab ∥cd; 4 ∵∠b ∠b ∠5 ∠ ab ∥ cd ∥ is eligible for ab ∥cd as 134. Option c. Methodological summary: the method of determining the two straight lines in parallel, in addition to using the decision theorem of the parallel lines, sometimes needs to be combined with the application of "two straight lines parallel to the same line" as shown, mf⊥nf⊥2=50° for f, mf⊥2=50° for f, nf=cd at point g, ∠1=140°, ∠2=50° for the determination of the position of ab and cd, and for the justification ... Decomposition: nfq=mfq=50° =40° for the observation map. Mfq=2=50° for the left, so that sfq=40° for the +1=nq=180° so that the ab∥cdq method is summed up: in the resolution of the problem with the parallel line, appropriate support lines are sometimes required. Question two: the practical application of the parallel line: a car travelling on the road, turning twice, still moving in the same direction, may be () a. Turning 60° right for the first turn, 120° b right for the second turn, 60° right for the second turn, 60° right for the second turn, 120° d right for the second turn, 60° right for the second turn, 60° left for the second turn, and 60° left for the second turn: after the car turning twice, the route and the original route must not be the same as the line, but in the same direction, indicating that the course should be parallel. As shown, if the first turn to the right, then the second turn to the left, the second to the opposite and the second to the same angle, the second to the same angle, so that the course is parallel and the direction remains the same. The d. Method should be chosen to sum up: using mathematical knowledge to solve practical problems, the key is to correctly transform practical problems into mathematical ones, i. E., drawing the intent or column expression, and then solving the mathematical problems, and then finally returning to the actual ... Iii. The method of determining the parallel lines of the design of the book: 1. The same azimuth, with two straight lines; the same internal wrong angles, with two straight lines parallel; complementarity with the inner corners, with two straight lines parallel to the same line. In teaching design, highlighting students as subjects of learning, leaving as much of the problem as possible to the students, consciously penetrating students into “transforming” ideas and linking mathematics learning to life. This class is a difficult start for students in the seventh grade, and it is time to remind students where they should be, to prove that they must be rigorous, to justify their steps and to prevent students from using previously learned conclusions as a basis for proof only on the basis of the definition of the concept, the required justice and the reasoning of proof, and to prevent students from using previously learned conclusions as evidence in the second class without conceiting. In the search for conclusions, experience the pleasure of exploration, enhance confidence in mathematics learning, and feel the joy of success. [teach focus] masters cosine, tangent concepts, and can use them to solve specific problems. [teaching difficulty] uses the definitions of trigonometric functions in a flexible manner to calculate., first, situational import, preliminary understanding questions. [pedagogical notes] this set-up of issues is both a recollection of the important knowledge of the last class and a preparation for the introduction of this section of knowledge, and implies that the solution to the problem is exactly the same as the approach to drawing conclusions from the last class, allowing students to communicate with one another, teachers to visit, listen to their views, opinions, participate in discussions at all times, and help students to acquire the correct perception ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What about the opposite side and the next side? After the students have concluded, the cosine should be summarised together with the students. ... Cosine: in rtabc, ∠c=90°, we call ∠a the cosa, or cosa = positive: in rtaabc, ∠c=90°, ∠c = positive, ∠c = 90°, 锐c = positive, tana = positive, tana = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = . This could be done independently of the student, with the teacher visiting the guide, while paying attention to whether the student can be narrowly defined when solving the problem, i. E. Whether the use of the sina =, cosa =, tanb = is appropriate and whether there is any confusion. Example 2 in abc, ab = ac = 20, bc = 30, test the value of tanb, sinc. [analysis] because ∠b and ∠c are not sharp angles in a straight-angled triangle, the value of tanb, sinc is requestedit's forcing us to..
