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View attachment 79889 gíup mình câu c,d e nha
c) $(7-\sqrt x)(8-\sqrt x) = x+11$.
ĐKXĐ: $x \geqslant 0$.
pt $\Leftrightarrow 56-15\sqrt x+x=x+11 \Leftrightarrow 15\sqrt x=45 \Leftrightarrow \dots$
d) $\sqrt{4x-8}+5\sqrt{x-2}-\sqrt{9x-18}=20$.
ĐKXĐ: $x \geqslant 2$.
pt $\Leftrightarrow 2\sqrt{x-2}+5\sqrt{x-2}-3\sqrt{x-2}=20 \Leftrightarrow 4\sqrt{x-2}=20 \Leftrightarrow \dots$
e) $5\sqrt{x-1} - \sqrt{36x-36} + \sqrt{9x-5}=\sqrt{8x+12}$
ĐKXĐ: $x \geqslant 1$.
pt $\Leftrightarrow 5\sqrt{x-1} - 6\sqrt{x-1} + \sqrt{9x-5} = \sqrt{8x+12}$
$\Leftrightarrow \sqrt{8x+12} + \sqrt{x-1} = \sqrt{9x-5}$
Ta có: $VT=\sqrt{8x+12} + \sqrt{x-1} \geqslant \sqrt{8x+12+x-1} =\sqrt{9x+11} > \sqrt{9x-5} =VP$.
=> pt vô nghiệm.