Question

If the magnitude of the vectors a,b and c are 6,8,10 units respectively and if a+b=c,then the angle between a and c is

Answer 1

(a+b).c=c.c=c2
a.c+b.c =100........................1
(a+b). a= a.c
a.a+b.a=a.c
36 +b.a=a.c............................2
(a+b). b=c.b
a.b +b.b=c.b
a.b+ 64 =c.b...........................3
Now put the value of c.b from 1 then from 2 and 3 u find a.c
Then angle between a and c
Cosx= a.b /ab