Даны векторы 𝑎 → ( 5 ; 4 ) ${\displaystyle \stackrel{\to }{a}\left(5;4\right)}$ и 𝑏 → ( 8 ; − 9 ) . ${\displaystyle \stackrel{\to }{b}\left(8;-9\right).}$ Найдите скалярное произведение 𝑎 → ⋅ 𝑏 → . ${\displaystyle \stackrel{\to }{a}\cdot \stackrel{\to }{b}.}$