Double Angle Identities (Grade 12 NSC Matric Mathematics): Flashcards

Find trig values of 2α using values of α

From compound angle formulae, set both angles equal

$2 \sin α \cos α$

$\cos^2 α - \sin^2 α$

$1 - 2 \sin^2 α$

$2 \cos^2 α - 1$

Three

$\sin^2 α + \cos^2 α = 1$

Use form that makes calculation easiest

Denominators = 0 or $\tan θ$ undefined