Edexcel A Level Maths: Pure:复习笔记5.6.1 Compound Angle Formulae

What are the compound angle formulae?

• There are six compound angle formulae (also known as addition formulae), two each for sin, cos and tan:
• For sin the +/- sign on the left-hand side matches the one on the right-hand side

• For cos the +/- sign on the left-hand side is opposite to the one on the right-hand side

• For tan the +/- sign on the left-hand side matches the one in the numerator on the right-hand side, and is opposite to the one in the denominator

• You can derive the tan identity by:
  • Writing
  • Dividing the numerator and denominator by