Answer
D
Work Step by Step
We are given that $t=\dfrac{\pi}{4}$.
In order to get the values of $x$ and $y$, we need to substitute the value of $t$ in the expression of $x$ and $y$.
$x= \cos (\dfrac{\pi}{4}) =\dfrac{1}{\sqrt 2}=\dfrac{\sqrt 2}{2} $
and $y=\sin (\dfrac{\pi}{4}) =\dfrac{1}{\sqrt 2}=\dfrac{\sqrt 2}{2} $
Thus, we have: $(x,y)=(\dfrac{\sqrt 2}{2}, \dfrac{\sqrt 2}{2})$
This matches with option $D$.
