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Flashcards · Maths · Further Trigonometry

The Cosine Rule

16 cards

  1. What is the cosine rule for a side?

    \(a^2 = b^2 + c^2 - 2bc\cos A\).

  2. What is the cosine rule for an angle?

    \(\cos A = \dfrac{b^2 + c^2 - a^2}{2bc}\).

  3. When do you use the cosine rule?

    With two sides and the included angle, or with three sides.

  4. Which side is \(a\) in the formula?

    The side opposite angle \(A\).

  5. What is \(\cos 60^\circ\)?

    \(\dfrac{1}{2}\).

  6. What is \(\cos 120^\circ\)?

    \(-\dfrac{1}{2}\).

  7. What is \(\cos 90^\circ\)?

    0.

  8. What does the cosine rule become when \(A = 90^\circ\)?

    Pythagoras' theorem.

  9. What does a negative cosine tell you about the angle?

    It is obtuse.

  10. Which angle is the largest in a triangle?

    The one opposite the longest side.

  11. What is \(\cos 30^\circ\)?

    \(\dfrac{\sqrt{3}}{2}\).

  12. What is \(\cos 45^\circ\)?

    \(\dfrac{\sqrt{2}}{2}\).

  13. Which step comes before the square root when finding a side?

    Finding \(a^2\).

  14. Is the sine rule or cosine rule used for three sides?

    The cosine rule.

  15. What should you write before simplifying?

    The rule with the numbers substituted.

  16. What do the angles of a triangle add up to?

    \(180^\circ\).