a. cos(a→,b→)=−3.2+1.632+12.22+62=0
=> (a→,b→)=90o.
b. cos(a→,b→)=3.2+1.432+12.22+42=12
=> (a→,b→)=45o.
c. cos(a→,b→)=−2.2+1.(−2)2+12.22+2=−1
=> (a→,b→)=180o.