Topic 3: Circular Functions and Trigonometry

Introduction

"The aims of this topic are to explore the circular functions and to solve problems using trigonometry. On examination papers, radian measure should be assumed unless otherwise indicated."

- From IB Math SL Guide

Circle

Radian Measure

There are 2π radians in a complete circle, and π radians in a half circle. Therefore as there are 360 degrees in a complete circle, and 180 degrees in a half circle, we can derive this equation to convert

Degrees = Radians * 180/π

Radians = Degrees * π/180

Length of an arc

The length of an arc is equal to s=r(θ), where r= radius, (θ)=inscribed angle in radians, and s=the length of the arc.

This formula is synonymous with the formula for the circumference of a circle where (theta)=2(pi).

Area of a Sector

A = (1/2)(θ)(r^2) where r is the radius.

Cosine and Sine (relative to Unit Circle)

sinθ=y cosθ=x tanθ=y/x CAST Beginning from the IV section will let you know which are positive (Cosine, All, Sine, Tangent)

Quadrant	SIN	COS	TAN
I	+	+	+
II	+	-	-
III	-	-	+
IV	-	+	-

Double Angle Formulae

sin2(θ)= 2sin(θ)cos(θ)

cos2(θ)= cos^2(θ)-sin^2(θ)= 2cos^2(θ)-1=1-2sin^2(θ)

Triangles

Area

Area of a triangle = (1/2) ab sin C