Mathematics

Problem

Let

\mathbf{a}=\langle t,1,3\rangle

and

\mathbf{b}=\langle 2,-1,t\rangle

. If the angle between

\mathbf{a}

and

\mathbf{b}

90^{\circ}

, the value of

t

is a)

-\dfrac{1}{5}

0

\dfrac{1}{5}

\dfrac{1}{3}