3. , , .
, , , . .
: , .
, . :
, , . .
.
, , , . ., ( ) . , .
.
4. (. angulus ) , , . , . , , , .
360 , 1/360 (. gradus , ), ( ). , 1 = 1/360 .
1/360 * 360 = 1 * 360 = 360.
, , 360 .
5. , . 180.
( , ) , 360: 2 = 180.
( ) , 360: 4 = 90.
6. , 90,
7. , .
, .
8. , 90 (.. ).
: 0 90.
9. , 90, 180 (.. , ).
135
10. , , .. .
= =1/2
11. ( . bi - "", sectio - "") , ()
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12. , , , . 180.
∠ + ∠ = 180.
13. (. verticalis ), . .
∠=∠COD, ∠ = ∠ OD.
14. , ( - . perpendicularis ).
A D ∠ 1 = ∠ 2 = ∠ 3 = ∠ 4 = 90, A ⊥ D.
, , .
∠ = 90, ⊥ .
( ) ⊥.