a)
notez unghiurile congruiente cu x si celalalt va fi y
2x+y=180
x+y=142⇒y=142-x
2x+142-x=180
x=180-142
x=38
y=142-38
y=104
b)
x+y=38
x+2y=180
2y+38-y=180
y=180-38
y=142
x=(180-142):2= 19
c) x+y=60
2y+x=180
2y+60-y=180
y=120
x=(180-120):2=30
d)
x+y=100
2x+y=180
2x+100-x=180
x=80
y=(180-80):2=50