Số lẻ bé nhất có 2 chữ số là: 11

Số lẻ lớn nhất có 3 chữ số là: 999

Số bé là:

(999 - 11) : 2 = 494

Số lớn là:

999 - 494 = 505

\(a.\dfrac{1}{4}+\dfrac{3}{4}x=-0,3\)

\(\Leftrightarrow\dfrac{3}{4}x=-\dfrac{11}{20}\)

\(\Leftrightarrow x=-\dfrac{11}{15}\)

\(b.\dfrac{4}{7}x-\dfrac{7}{3}=\dfrac{1}{21}\)

\(\Leftrightarrow\dfrac{4}{7}x=\dfrac{50}{21}\)

\(\Leftrightarrow x=\dfrac{25}{6}\)

C

\(\dfrac{\sqrt{x}}{\sqrt{x}-1}\ge0\left(đkxđ:x\ne1;x\ge0\right)\)

\(\Leftrightarrow\sqrt{x}\ge0\)

\(\Leftrightarrow x\ge0\)

Vậy ...

Thay m = 1 vào pt, ta đc:

\(x-2\left(1+1\right)\sqrt{x}+1+4=0\)

\(\Leftrightarrow x-4\sqrt{x}+5=0\)

Đặt \(\sqrt{x}=t\left(t\ge0\right)\), ta được:

\(t^2-4t+5=0\)

\(\Delta'=\left(-2\right)^2-5=-1\)

Do \(\Delta'< 0\) nên pt vô nghiệm

\(\left[\dfrac{3x+3\sqrt{x}-3}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}+\dfrac{1}{\sqrt{x}+2}-\dfrac{\sqrt{x}-2}{\sqrt{x}-1}\right]:\dfrac{\sqrt{x}}{\sqrt{x}+1}\left(x>0;x\ne1\right)\)

\(=\left[\dfrac{3x+3\sqrt{x}-3}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}+\dfrac{\sqrt{x}-1}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}-\dfrac{x-4}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}\right].\dfrac{\sqrt{x}+1}{\sqrt{x}}\)

\(=\dfrac{3x+3\sqrt{x}-3+\sqrt{x}-1-x+4}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}.\dfrac{\sqrt{x}+1}{\sqrt{x}}\)

\(=\dfrac{2x+4\sqrt{x}}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}.\dfrac{\sqrt{x}+1}{\sqrt{x}}\)

\(=\dfrac{2\sqrt{x}\left(\sqrt{x}+2\right)}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}.\dfrac{\sqrt{x}+1}{\sqrt{x}}\)

\(=\dfrac{2\sqrt{x}+2}{\sqrt{x}-1}\)

\(\dfrac{15}{7}+15\ne\dfrac{15}{22}\) em nhé

Nửa chu vi: 7 + 15 = 22 (cm)

Tỉ số = 15/22 

Chọn D