Identities & Equations

 

 

 

Contents

 

Basic Identities

 

Second Degree Identities

 

Simple Equations

 

Second Degree Equations

  

Quiz 

 

 

Trigonometry Main Page

 

 

Second Degree Equations

This type of equations involves the square of the ratios, hence it is more complex to solve. This is where all the identities you have learnt will come in.

 

Example 1

Solve for x between 0° and 360° for the equation 6 sin2 x = 6 - 6 cos2 x

6 sin2x = 6 - 6 cos2x   (recall sin2 q to cos2 q = 1)

6 - 6 cos2x + cos x - 4 = 0

2 - 6 cos2 x + cos x = 0

(2 - 3 cos x)(1 + 2 cos x) = 0

basic angle = 60° or 48.19°

x = 48.19°, 311.81°, 120° or 240°

Example 2

Solve for x between 0° and 360° for the equation 2 cot2 x + 11 = 9 cosec x

2 cot2 x + 11 = 9 cosec x

    2 cosec2 x - 2 + 11 = 9 cosec x

    2 cosec2 x - 9 cosec x + 9 = 0

    (2 cosec x - 3)(cosec - 3) = 0

    cosec x = 3/2 or 3

    sin x = 2/3 or 1/3

    basic angle = 41.81° or 19.41°

    x = 19.4°, 160.5°, 138.2° or 41.8°