Trigonometry and precalculus
Trig identities and examples

Trigonometric identities

  1. Trigonometric Identities
  2. Pythagorean identities
  3. Proof: sin(a+b) = (cos a)(sin b) + (sin a)(cos b)
  4. Proof: cos(a+b) = (cos a)(cos b)-(sin a)(sin b)
  5. Trig identities part 2 (part 4 if you watch the proofs)
  6. Trig identies part 3 (part 5 if you watch the proofs)
  7. Addition and subtraction trig identities
  8. Law of cosines
  9. Law of cosines
  10. Navigation Word Problem
  11. Proof: Law of Sines

Law of cosines Solve missing triangle measures using the law of cosines