So I understand where the formula for cos between two vectors comes from. However, if i have a paralelogram of basis $\overrightarrow{a}$,$\overrightarrow{b}$ , and i want to find out the angle between its diagonals starting only from the fact that

$\Vert \overrightarrow{a}\Vert =3$

and

$\Vert \overrightarrow{b}\Vert =2$

and the angle between them pi/3 , how would i go about it?

I know the diagonals are $\overrightarrow{a}-\overrightarrow{b}$ and $\overrightarrow{a}+\overrightarrow{b}$ respectively, but im not sure how I shoul apply the formula for sum and difference of vectors.

$\Vert \overrightarrow{a}\Vert =3$

and

$\Vert \overrightarrow{b}\Vert =2$

and the angle between them pi/3 , how would i go about it?

I know the diagonals are $\overrightarrow{a}-\overrightarrow{b}$ and $\overrightarrow{a}+\overrightarrow{b}$ respectively, but im not sure how I shoul apply the formula for sum and difference of vectors.