Master Trigonometry with These Essential Practice Questions

[Michael_Light]

 

[LCKurtz]

Try this:

$-1\le \cos x \le 1$

$-\frac 5 4 \le \cos x - \frac 1 4 \le \frac 3 4$

$0\le (\cos x - \frac 1 4)^2 \le \frac {25} {16}$

$0\ge -2(\cos x - \frac 1 4)^2\ge -\frac {25} 8$

$\frac 9 8 \ge \frac 9 8 -2(\cos x - \frac 1 4)^2\ge -\frac {16} 8 = -2$

Think about what that gives.