$\frac{d}{dx} (\cos \frac{1}{x})$ এর মান কোনটি? Dinajpur • 2023 ক (ক) $-\frac{1}{x^2} \cos \frac{1}{x}$ খ (খ) $-\frac{1}{x^2} \sin \frac{1}{x}$ গ (গ) $\frac{1}{x^2} \sin \frac{1}{x}$ ঘ (ঘ) $\frac{1}{x^2} \cos \frac{1}{x}$