Teacher measurement and control P39.

2.3 "isosceles triangle"

first kind

Pre-learning principle

① axis; Symmetry axis; Coincidence; Three lines in one; Equiangular phenomenon

② Three; Are all equal; 60

Pre-learning perception

1.70 2. 120

Shi Ming navigation

Example 1 Solution: ab = ad = dc, ∴∠ CAD = ∠ C, ∠ B = ∠ ADB = ∠ CAD+∠ C. Let ∫c = x, ∴.

Example 2 proves that ∵△ABC is an equilateral triangle, ∵BD is the center line of the AC side, ∴BD bisects ∠ABC, ∴ ∠ DBE = 1/2 ∠ ABC = 30. ∵CD=CE,∴∠CDE=∠E。 And acb = 60, and ∠ACB is the outer angle of △CDE, ∠ CDE+∠ E = 60, ∠ CDE = ∠ E = 30, ∠

class exercise

1.d2.1003. 16㎝,16 ㎝, 22㎝ or 20㎝, 20㎝,/kloc-