Question Number 187871 by mustafazaheen last updated on 23/Feb/23
$${how}\:{is}\:{solution} \\ $$$$\mathrm{sgn}\left(\mathrm{cos}\frac{\mathrm{21}}{\mathrm{10}}\right)=? \\ $$
Answered by mr W last updated on 23/Feb/23
$$\frac{\mathrm{21}}{\mathrm{10}}=\mathrm{2}.\mathrm{1}\:>\frac{\pi}{\mathrm{2}}\:{but}\:<\pi \\ $$$$\Rightarrow\mathrm{cos}\:\frac{\mathrm{21}}{\mathrm{10}}\:<\mathrm{0} \\ $$$$\Rightarrow{sgn}\left(\mathrm{cos}\:\frac{\mathrm{21}}{\mathrm{10}}\right)=−\mathrm{1} \\ $$