$\text { The cartesian equation of the curve given by } x=6 \cos \theta, \quad y=6 \sin \theta \text { is }$ (A) $x^{2}+y^{2}=36$ (B) $x^{2}+y^{2}=5$ (C) $x^{2}+y^{2}=25$ (D) $x^{2}+y^{2}=6$

The correct option is option (A)

$\begin{array}{l}
x=6 \cos \theta ; \quad y=6 \sin \theta \\
\cos ^{2} \theta+\sin ^{2} \theta=1 \\
\cos \theta=\frac{x}{6} \quad ; \sin \theta=\frac{y}{6} \\
=> \frac{x^{2}}{36}+\frac{y^{2}}{36}=1 \\
=> x^{2}+y^{2}=36
\end{array}
$