Trigonometric Identities Sun and Differences Of Angles

Distance Formula:
Let P(x₁ , y₁) and Q(x₂ , y₂) be two points. If "d" denotes the distance between them,
then

i.e., square root of the sum of square the difference of x-coordinates and square the difference of y-coordinates.

Fundamental Law Of Trigonometry:

Let α and β any two angles (real numbers), then

cos(α - β) = cosα cosβ + sinα sinβ

which is called the Fundamental Law Of Trigonometry.