Write the principal value of cos−1(−21)−2sin−1(−21).Answer: πSolutioncos−1(−21)=32π (angle in [0,π]) and sin−1(−21)=−6π (angle in [−2π,2π]).cos−1(−21)−2sin−1(−21)=32π−2(−6π)=32π+3π=ππCBSE Class 12 Board · 2012 · Subjective