Vectors

• Position vectors

  $\vec{AB}=$ $\underline{b}-\underline{a}$
• If $\underline{a}=$$\underline{x_i}+$$\underline{y_j}+$$z\underline{k}$ then

  $\left|\underline{a}\right|=$ $\sqrt{x^2+y^2+z^2}$
• Unit vector

  $\hat{\underline{a}}\ =$ $\frac{1}{\left|\underline{a}\right|}\underline{a}$
• Angles with axes:

  $\cos\theta_x=$ $\frac{x}{\left|\underline{a}\right|}$
• Angles with axes:

  $\cos\theta_z=$ $\frac{z}{\left|\underline{a}\right|}$