Tìm nguyên hàm của hàm số \(f(x) = c{\rm{os}}\,{\rm{2x}}{\rm{.}}\)
A. \(\int {f(x)dx} = \frac{1}{2}{\rm{sin}}\,{\rm{2x}}\,{\rm{ + }}\,{\rm{C}}\)
B. \(\int {f(x)dx} = - \frac{1}{2}{\rm{sin}}\,{\rm{2x}}\,{\rm{ + }}\,{\rm{C}}\)
C. \(\int {f(x)dx} = 2{\rm{sin}}\,{\rm{2x}}\,{\rm{ + }}\,{\rm{C}}\)
D. \(\int {f(x)dx} = - 2{\rm{sin}}\,{\rm{2x}}\,{\rm{ + }}\,{\rm{C}}\)