$\begin{array}{l} 1){x^4} - 7{x^2} + 12 = 0\\  \Leftrightarrow {x^4} - 3{x^2} - 4{x^2} + 12 = 0\\  \Leftrightarrow {x^2}({x^2} - 3) - 4({x^2} - 3) = 0\\  \Leftrightarrow ({x^2} - 3)({x^2} - 4) = 0\\  \Leftrightarrow \left[ \begin{array}{l} {x^2} - 3 = 0\\ {x^2} - 4 = 0 \end{array} \right.\\  \Leftrightarrow \left[ {\begin{array}{*{20}{c}} {x =  - \sqrt 3 }\\ {x = \sqrt 3 }\\ {x =  - 2}\\ {x = 2} \end{array}} \right.\\ 2)\sqrt {14 - 2x}  = x - 3\\ Dk:x \le 7\\  \Leftrightarrow \left\{ {\begin{array}{*{20}{c}} {x - 3 \ge 0}\\ {14 - 2x = {{(x - 3)}^2}} \end{array}} \right.\\  \Leftrightarrow \left\{ \begin{array}{l} x \ge 3\\ 14 - 2x = {x^2} - 6x + 9 \end{array} \right.\\  \Leftrightarrow \left\{ \begin{array}{l} x \ge 3\\ {x^2} - 4x - 6 = 0 \end{array} \right.\\  \Leftrightarrow \left\{ {\begin{array}{*{20}{c}} {x \ge 3}\\ {\left[ {\begin{array}{*{20}{c}} {x = 2 + \sqrt {10} }\\ {x = 2 - \sqrt {10} } \end{array}} \right.} \end{array}} \right.\\  \Rightarrow x = 2 + \sqrt {10}  \end{array}$