Find the value of sin⁻¹(-1/2) + cos⁻¹(-1/2) + tan⁻¹(-1)…

Step 1. The three values. $\sin^{-1}\left(-\dfrac{1}{2}\right) = -\dfrac{\pi}{6}$, $\cos^{-1}\left(-\dfrac{1}{2}\right) = \dfrac{2\pi}{3}$ and $\tan^{-1}(-1) = -\dfrac{\pi}{4}$.

Step 2. Add. Over the denominator $12$ the angles are $-\dfrac{2\pi}{12}$, $\dfrac{8\pi}{12}$ and $-\dfrac{3\pi}{12}$. The sum is $\dfrac{3\pi}{12} = \dfrac{\pi}{4}$.

Step 3. As numbers. $\dfrac{\pi}{4} = 0.7854$ radians, and $0.7854 \div \pi = 0.25$.