Question

2√x-1 - √4x-4 - √9x-9 = 20

Answer 1

\(ĐK:x\ge1\\ PT\Leftrightarrow2\sqrt{x-1}-2\sqrt{x-1}-3\sqrt{x-1}=20\\ \Leftrightarrow\sqrt{x-1}=-\dfrac{20}{3}\Leftrightarrow x\in\varnothing\)

Answer 2

ĐKXĐ: \(x\ge1\)

\(pt\Leftrightarrow2\sqrt{x-1}-2\sqrt{x-1}-3\sqrt{x-1}=20\)

\(\Leftrightarrow-3\sqrt{x-1}=20\)

\(\Leftrightarrow\sqrt{x-1}=-\dfrac{20}{3}\)(vô lý do \(\sqrt{x-1}\ge0\forall x\))

Vậy \(S=\varnothing\)