$C$ and $D$ are points with position vectors $c$ and $d$ respectively. If the magnitude of $c=5$ and magnitude of $d=7$, and the dot product; $c\cdot d=4$. Find $|CD|$ (vector connecting $C$ and $D$)
I have tried $\cos \theta=\frac{4}{35}$ And substituted the angle into $a^2=7^2+5^2-2(7)(5)\cos \theta$ I got the wrong answer so i tried again but this time with $180-\theta$ for the angle but I still can't get an answer in exact form
$\sqrt{66}$
which renders as $\sqrt{66}$. All the best. $\endgroup$