FRAC{1}{x} \right)}^{2}}\ge 0,\,\,\TEXT{}\,\,x\in R,\] we have \[{{x}^{2}}+\frac{1}{{{x}^{2}}}\ge 2\] and HENCE, \[F(x)={{\cos }^{2}}x+\frac{1}{{{\cos }^{2}}x}\ge 2\].