Question

the unit vector is represented by 0.5 i + 0.8 J + c k then what is the value of c

Answer 1

Hence √0.5^2+0.8^2+c^2 =1=> 1=0.25+0.64+c^2 =>
c^2 =1-0.89=0.11=> c=√0.11 =0.3316 .Value of c=0.3316.

Answer 2

Here is your answer mate:

|a+b+c|=1
√0.5²+0.8²+c²=1
squaring both sides 
0.5²+0.8²+c²=1
0.25+0.64+c²=1
c²+0.89=1.00
c²=0.11
c=√0.11

Thanks,

Niki..... :-)