Topic explanation

Standard explanation

Put B=A. Three forms of cos 2A are all useful (pick the one that matches sin or cos on the paper). Half-angle later if asked via rearranging cos 2A.

Key points

• B=A
• tan(A+B)=s+t1-st
• sin 2A = 2 sin A cos A
• minus in tan(A+B) bottom
• DOUBLE-ANGLE FORMULAS: Put B=A. Three forms of cos 2A are all useful (pick the one that matches sin or cos on the paper). H
• DOUBLE: Put B=A.
• WHAT — DOUBLE-ANGLE FORMULAS: Put B=A. Three forms of cos 2A are all useful (pick the one that matches sin or cos on the paper). H
• WHY — Why it matters: This rule is a separate learning unit inside tan(a±b) and double angle. It can be defined, applied,

Labelled diagram