Initial side of an angle - trigonometry

In trigonometry an angle is usually drawn in what is called the "standard position" as shown below.

In this position, the vertex of the angle (B) is on the origin of the x and y axis. One side of the angle is always fixed along the positive x-axis - that is, going to the right along the axis in the 3 o'clock direction (line BC). This is called the initial side of the angle.

The other side of the angle is called the terminal side.

See also Angle definition and properties - Trigonometry

Other trigonometry topics

Angles

• Angle definition, properties of angles
• Standard position on an angle
• Initial side of an angle
• Terminal side of an angle
• Quadrantal angles
• Coterminal angles
• Reference angle

Trigonometric functions

• Introduction to the six trig functions
• Functions of large and negative angles
• Inverse trig functions
• SOH CAH TOA memory aid


• Sine function (sin) in right triangles
• Inverse sine function (arcsin)
• Graphing the sine function
• Sine waves


• Cosine function (cos) in right triangles
• Inverse cosine function (arccos)
• Graphing the cosine function


• Tangent function (tan) in right triangles
• Inverse tangent function (arctan)
• Graphing the tangent function


• Cotangent function cot (in right triangles)
• Secant function sec (in right triangles)
• Cosecant function csc (in right triangles)

Solving trigonometry problems

• The general approach
• Finding slant distance along a slope or ramp
• Finding the angle of a slope or ramp

Calculus

• Derivatives of trigonometric functions