Theory question 102
Trigonometry(a) If 9 cos x° − 7 = 1 and 0° ≤ x ≤ 90°, find x.
(b) Given that x is an integer, find the three greatest values of x which satisfy the inequality 7x < 2x − 13.
Show the model answer
Model answer
(a) 9 cos x = 8 → cos x = 0.8889 → x ≈ 27.3°.
(b) 5x < −13 → x < −2.6. The three greatest integers are −3, −4 and −5.
Explanation
Be careful: the greatest integers less than −2.6 are −3, −4, −5.