Paper 2 · Trigonometry Lesson 10 of 13

Trigonometry 4.9 – Trig proof 5

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You’ll learn

  • Prove cos(A + B) = cos A cos B − sin A sin B by substituting −B into cos(A − B)
  • Use the even/odd identities cos(−B) = cos B and sin(−B) = −sin B

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