Question 20 pleaseeeee

Dear student,


Given, a=xi+(x−1)j+k and b=(x+1)i+j+ak

Therefore, a⋅b=[xi+(x−1)j+k]⋅[(x+1)i+j+ak]

=x(x+1)+x−1+a=x^2+2x+a−1

We must have a⋅b>0,∀xϵR

⇒x^2+2x+a−1>0,∀xϵR

⇒4−4(a−1)<0                      

⇒a>2


Regards