The length of the vector <-4,-3> is
[tex]\sqrt{(-4)^2+(-3)^2}=\sqrt{16+9}=\sqrt{25}=5[/tex]
So, if we divide the components by 5, we'll get a vector with unitary length:
[tex]v=\left(-\dfrac{4}{5}, -\dfrac{3}{5}\right) \implies |v| = \sqrt{\left(-\dfrac{4}{5}\right)^2+\left(-\dfrac{3}{5}\right)^2}=\sqrt{\dfrac{16}{25}+\dfrac{9}{25}}=\sqrt{\dfrac{25}{25}}=1[/tex]