77.
a) \(2x-3-\sqrt{9-12x+4x^2}\)
\(=2x-3-\sqrt{3^2-2.3.2x+\left(2x\right)^2}\)
\(=2x-3-\sqrt{\left(3-2x\right)^2}\)
\(=2x-3-\left|3-2x\right|\)
\(=2x-3-3+2x\) (vì \(x< \dfrac{3}{2}\) nên 3 - 2x > 0)
\(=4x-6\)
b) \(\sqrt{x^2-4x+4}-\sqrt{x^2+4x+4}\)
\(=\sqrt{x^2-2.2.x+2^2}-\sqrt{x^2+2.2.x+2^2}\)
\(=\sqrt{\left(x-2\right)^2}-\sqrt{\left(x+2\right)^2}\)
\(=\left|x-2\right|-\left|x+2\right|\)
\(=2-x-x+2\) (vì \(x\ge-2\) nên \(x+2\ge0\), vì \(x\le2\) nên \(x-2\le0\))
\(=4-2x\)
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