Răspuns:
12.
a+b=90° (unghiuri complementare)
a/b = 5/13 =>a=5b/13
5b/13 + b = 90°
5b + 13b = 1170
18b=1170
b=65° =>a=25°
15.
a)180°-45°=135°
b)180°-137°=43°
c)179°60'-110°20'=69°40'
d)179°59'60"-65°3'29"=114°56'31"
16.
a)90°:2=45°
b)180°:2=90° (unghi drept)
17.
a+b=180°
a=3b
4b=180° =>b=45° =>a=135°
18.
a+b=180°
a=24+b
24+2b=180°
2b=156°
b=78° =>a=102°
