Let's begin by listing out the information given to us:
Triangle OA gives us the triangle with angle 60°
A (0.5, 0.8660)
That means that: adjacent = 0.5, opposite = 0.8660
hypotenuse² = 0.8660² + 0.5² = 1 ⇒ hypotenuse = 1
We will solve for the trigonometric identities as shown below:
tan θ = opposite ÷ adjacent ⇒ tan 60° = 0.8660 ÷ 0.5 = 1.732
tan 60° = 1.732
sin θ = opposite ÷ hypotenuse ⇒ sin 60° = 0.8660 ÷ 1 = 0.8660
sin 60° = 0.8660
cos θ = adjacent ÷ hypotenuse ⇒ cos 60° = 0.5 ÷ 1 = 0.5
cos 60° = 0.5