dalam sebuah titik K (12,9),maka cos B ...

K(12,9) => x = 12, y = 9
r = √(12^2 + 9^2) = √(144 + 81) = √225 = 15
Cos Beta = x/r = 12/15 = 4/5

Titik K (12,9)
OK' = x = 12
KK' = y = 9
OK² = OK'² + KK'² = 12² + 9² = 225
OK = √225 = 15
β = sudut OK dengan sumbu x
cos β = OK'/OK = 12/15 = 4/5 = 0,8