Giải các phương trình sau:
\(a) \, \, \,{x^2} - 5x + 4 = 0 \)
\(b) \, \,{x^4} + {x^2} - 6 = 0 \)
A.\(\begin{array}{l}a)\,\,S = \left\{ { - 1;\,\,4} \right\}.\\b)\,\,S = \left\{ { - 2;\,\,2} \right\}.\end{array}\)
B.\(\begin{array}{l}a)\,\,S = \left\{ {1;\,\,4} \right\}.\\b)\,\,S = \left\{ { - \sqrt 2 ;\,\,\sqrt 2 } \right\}.\end{array}\)
C.\(\begin{array}{l}a)\,\,S = \left\{ {1;\,\, - 4} \right\}.\\b)\,\,S = \left\{ { - 2;\,\,2} \right\}.\end{array}\)
D.\(\begin{array}{l}a)\,\,S = \left\{ { - 1;\,\, - 4} \right\}.\\b)\,\,S = \left\{ { - \sqrt 2 ;\,\,\sqrt 2 } \right\}.\end{array}\)