Written working: choosing a cosine double-angle identity
Student Activity 𝅛 Identity Decision 𝅛 Exam-quality Working 𝅛 Follow-up ⭕ Learning Focus SL and HL students: (no additional HL content) • selecting an equivalent identity for a specific purpose • eliminating constants efficiently • avoiding random substitution • stating domain restrictions when dividing • presenting a short, directed derivation The three forms of \displaystyle \cos2x are equivalent, but they are not...