To find positive coterminal angle we have to add 360 and to find negative coterminal angle, we have to subtract 360 degree.
a. 150 degree
Positive coterminal angle
[tex]150+360= 510 degree[/tex]
Negative coterminal angle
[tex]150-360=-210 degree[/tex]
b.-420 degree
Positive coterminal angle
[tex]-420+2*360=300 degree[/tex]
negative coterminal angle
[tex]-420-360 = -780 degree[/tex]