$\int \frac{xdx}{\sqrt{1-x^2}} = f(x) + c$ হলে f(x) = কত? Dinajpur • 2023 ক (ক) $\sin^{-1} x$ খ (খ) $\cos^{-1} x$ গ (গ) $\ln (\sqrt{1-x^2})$ ঘ (ঘ) $-\sqrt{1-x^2}$