Déterminant de $$$\left[\begin{array}{cc}\cos{\left(\theta \right)} & - r \sin{\left(\theta \right)}\\\sin{\left(\theta \right)} & r \cos{\left(\theta \right)}\end{array}\right]$$$
Calculatrice associée: Calculatrice de la matrice des cofacteurs
Votre saisie
Calculer $$$\left|\begin{array}{cc}\cos{\left(\theta \right)} & - r \sin{\left(\theta \right)}\\\sin{\left(\theta \right)} & r \cos{\left(\theta \right)}\end{array}\right|$$$.
Solution
Le déterminant d'une matrice 2x2 est $$$\left|\begin{array}{cc}a & b\\c & d\end{array}\right| = a d - b c$$$.
$$$\left|\begin{array}{cc}\cos{\left(\theta \right)} & - r \sin{\left(\theta \right)}\\\sin{\left(\theta \right)} & r \cos{\left(\theta \right)}\end{array}\right| = \left(\cos{\left(\theta \right)}\right)\cdot \left(r \cos{\left(\theta \right)}\right) - \left(- r \sin{\left(\theta \right)}\right)\cdot \left(\sin{\left(\theta \right)}\right) = r$$$
Réponse
$$$\left|\begin{array}{cc}\cos{\left(\theta \right)} & - r \sin{\left(\theta \right)}\\\sin{\left(\theta \right)} & r \cos{\left(\theta \right)}\end{array}\right| = r$$$A