4.6
D=9*9+16*9=225
Ответ: x∈[-1;3]
6.8
3} \atop {a\geq 3}} \right. \\\left \{ {\sqrt{a}\leq 3} \atop {\sqrt{a} \geq 2}} \right. \\\end{array}" alt="\left[\begin{array}{ccc}\left \{ {{\sqrt{a}>3} \atop {a\geq 3}} \right. \\\left \{ {\sqrt{a}\leq 3} \atop {\sqrt{a} \geq 2}} \right. \\\end{array}" align="absmiddle" class="latex-formula">
9} \atop {a\geq 3}} \right. \\\left \{ {0\leq a\leq 9} \atop {a \geq 4}} \right. \\\end{array}" alt="\left[\begin{array}{ccc}\left \{ {{a>9} \atop {a\geq 3}} \right. \\\left \{ {0\leq a\leq 9} \atop {a \geq 4}} \right. \\\end{array}" align="absmiddle" class="latex-formula">
9} \atop {4\leq 2^x\leq 9}} \right. \\\left \{ {{x>log2(9)} \atop {log2(4)\leq x\leq log2(9)}} \right. \\2\leq x" alt="\left \{ {{2^x>9} \atop {4\leq 2^x\leq 9}} \right. \\\left \{ {{x>log2(9)} \atop {log2(4)\leq x\leq log2(9)}} \right. \\2\leq x" align="absmiddle" class="latex-formula">
Ответ: [2;+∞)