WAEC 2009 · Paper 2 · Q2

(a)
If $9\cos x - 7 = 1$ and $0^\circ \le x \le 90^\circ$ , find $x$ .
(b)
Given that $x$ is an integer, find the three greatest values of $x$ which satisfy the inequality $7x < 2x - 13$ .
Separate values with commas, e.g. 3, −2

Worked solution (try it first)

Add 7 to both sides: $9\cos x = 8$ .
Divide by 9: $\cos x = \frac89 = 0.8889$ .
Use tables or a calculator in degree mode: $x = \cos^{-1}(0.8889) = 27.27^\circ$ .