a {-15;8}, |a| ___
b {8;-15}, |b| ___
c {30;-16}, |c| ___
d {16;-30}, |d| ___
|b|=sqrt(8^(2)+(-15)^(2))=sqrt(64+225)=sqrt(289)=17
|c|=sqrt(30^(2)+(-16)^(2))=sqrt(900+256)=sqrt(1156)=34
|d|=sqrt((-16)^(2)+30^(2))=sqrt(256+900)=sqrt(1156)=34