Todo triângulo, seja ele qual for, tem a som dos ângulos internos igual a 180°. Então:
a)
[tex]78+50+x= 180\\x= 180-78-89\\x= 52[/tex]
b)
[tex]\frac{5x}{2} +3x+48= 180\\\frac{5x}{2} +3x= 180-48\\\frac{5x}{2} +3x= 132\\2.(\frac{5x}{2} +3x)= (132).2\\5x+6x=264\\11x=264\\x= 24[/tex]
c)
[tex]30+x+2x+3x=180\\6x=180-30\\x=\frac{150}{6} \\x=25[/tex]
d)
[tex]x+39+45=180\\x=180-39-45\\x=96[/tex]
