
Trigonometry:
In a right angled OAB, where BOA = ,
i. sin = Perpendicular = AB ; Hypotenuse OB ii. cos = Base = OA ; Hypotenuse OB iii. tan = Perpendicular = AB ; Base OA iv. cosec = 1 = OB ; sin AB v. sec = 1 = OB ; cos OA vi. cot = 1 = OA ; tan AB 
Trigonometrical Identities:

sin^{2} + cos^{2} = 1.

1 + tan^{2} = sec^{2} .

1 + cot^{2} = cosec^{2} .


Values of Tratios:
0° (/6)
30°(/4)
45°(/3)
60°(/2)
90°sin 0 1 2 3 2 1 cos 1 3 2 1 2 0 tan 0 1 3 1 3 not defined 
Angle of Elevation:
Suppose a man from a point O looks up at an object P, placed above the level of his eye. Then, the angle which the line of sight makes with the horizontal through O, is called the angle of elevation of P as seen from O.
Angle of elevation of P from O = AOP.

Angle of Depression:
Suppose a man from a point O looks down at an object P, placed below the level of his eye, then the angle which the line of sight makes with the horizontal through O, is called the angle of depression of P as seen from O.