Question

Cho B=√x-1

1) Tìm x để B > 5

2) Tìm x nguyên để \(\dfrac{2}{B}\) nhận giá trị nguyên

Answer 1

\(1.B>5\Leftrightarrow\sqrt{x}-1>5\Leftrightarrow\sqrt{x}>6\Leftrightarrow x>36\)

\(2.ĐK:x\ge0;x\ne1\)

\(Để:\dfrac{2}{\sqrt{x}-1}\in Z\Leftrightarrow\left(\sqrt{x}-1\right)\in\left\{\pm1;\pm2\right\}\)

+)\(\sqrt{x}-1=1\Leftrightarrow x=4\left(TM\right)\)

+) \(\sqrt{x}-1=-1\Leftrightarrow x=0\left(TM\right)\)

+) \(\sqrt{x}-1=3\Leftrightarrow x=16\left(TM\right)\)

+) \(\sqrt{x}-1=-3\Leftrightarrow vô-n^o\)

KL.............