Find the principal value of sin−1(−21)+cos−1(−21).Answer: 2πSolutionFor any a∈[−1,1], sin−1a+cos−1a=2π. With a=−21:sin−1(−21)+cos−1(−21)=2π(Check: −6π+32π=2π.)2πCBSE Class 12 Board · 2010 · Subjective