[" 1.Find the domain of definition of "f(x)=cos^(-1)(x^(2)-4)" ."],[" 2.Find the domain of "f(x)=2cos^(-1)2x+sin^(-1)x" ."],[" 3.Find the domain of "f(x)=cos^(-1)x+cos x],[" 4.Find the principal value of each of the following: "],[[" (i) "cos^(-1)(-(sqrt(3))/(2))," [NCERT] "," (ii) "cos^(-1)(-(1)/(sqrt(2)))," (NCERT) "]]