Я не пойму одного в этом доказательстве. Что значит примерно подобен?
Там разные треугольники получаются
1. Calculate some known angles:
* ACB = 180-(10+70)-(60+20) = 20°
* AEB = 180-70-(60+20) = 30°
2. Draw a line from point D parallel to AB, labeling the intersection with BC as a new point F and conclude:
* DCF ACB
* CFD = CBA = 60+20 = 80°
* DFB = 180-80 = 100°
* CDF = CAB = 70+10 = 80°
* ADF = 180-80 = 100°
* BDF = 180-100-20 = 60°
3. Draw a line FA labeling the intersection with DB as a new point G and conclude:
* ADF BFD -
вот в этой строчке
* AFD = BDF = 60°
* DGF = 180-60-60 = 60° = AGB
* GAB = 180-60-60 = 60°
* DFG (with all angles 60°) is equilateral
* AGB (with all angles 60°) is equilateral
4. CFA with two 20° angles is isosceles, so FC = FA
5. Draw a line CG, which bisects ACB and conclude:
* ACG CAE
* FC-CE = FA-AG = FE = FG
* FG = FD, so FE = FD
6. With two equal sides, DFE is isosceles and conclude:
* DEF = 30+x = (180-80)/2 = 50