Question

If `(|a+b|)/(|a-b|)=1`, then the angle between `a` and `b` is
A. `0^(@)`
B. `45^(@)`
C. `90^(@)`
D. `60^(@)`

Answer 1

(c) `(|a+b|)/(|a-b|)=1`
or `|a+|=|a-b|`
or `sqrt(a^(2)+b^(2)+2ab cos alpha)=sqrt(a^(2)+b^(2)-2ab cos alpha)`
or `a^(2)+b^(2)+2ab cos alpha=a^(2)+b^(2)-2ab cos alpha`
or` 4ab cos alpha=0` or `cos alpha=0`
or `alpha=90^(@)`