Accedmychevron_right11thchevron_rightmathchevron_rightFunctions And Graphschevron_rightExercise 2.2

Solution

For graphing:

  • Use a small table of convenient xx values.
  • Note transformations (shifts, reflections, stretches).
  • State the domain restriction if a square root is involved.

(i) y=3xy=\sqrt{3x}

Domain: 3x0x03x\ge 0\Rightarrow x\ge 0.

Choose 3x3x as perfect squares: 3x=0,1,4,9,163x=0,1,4,9,16.

x013433163y=3x01234\begin{array}{c|ccccc} x & 0 & \frac{1}{3} & \frac{4}{3} & 3 & \frac{16}{3}\\ \hline y=\sqrt{3x} & 0 & 1 & 2 & 3 & 4 \end{array} Domain [0,),  Range [0,)\boxed{\text{Domain }[0,\infty),\;\text{Range }[0,\infty)}

(ii) y=x+5y=\sqrt{x}+5

Domain: x0x\ge 0.

x014916y=x+556789\begin{array}{c|ccccc} x & 0 & 1 & 4 & 9 & 16\\ \hline y=\sqrt{x}+5 & 5 & 6 & 7 & 8 & 9 \end{array}

This is y=xy=\sqrt{x} shifted up by 5.

Domain [0,),  Range [5,)\boxed{\text{Domain }[0,\infty),\;\text{Range }[5,\infty)}

(iii) y=12xy=-\dfrac{1}{2}\sqrt{x}

Domain: x0x\ge 0.

x014916y=12x0121322\begin{array}{c|ccccc} x & 0 & 1 & 4 & 9 & 16\\ \hline y=-\frac{1}{2}\sqrt{x} & 0 & -\frac{1}{2} & -1 & -\frac{3}{2} & -2 \end{array}

Reflection in xx-axis and vertical shrink by factor 12\frac{1}{2}.

Domain [0,),  Range (,0]\boxed{\text{Domain }[0,\infty),\;\text{Range }(-\infty,0]}

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

Domain: x+10x1x+1\ge 0\Rightarrow x\ge -1.

Choose x+1=0,1,4,9,16x+1=0,1,4,9,16.

x103815y=x+1+221012\begin{array}{c|ccccc} x & -1 & 0 & 3 & 8 & 15\\ \hline y=-\sqrt{x+1}+2 & 2 & 1 & 0 & -1 & -2 \end{array}

This is y=xy=\sqrt{x} shifted left by 1, reflected, then shifted up by 2.

Domain [1,),  Range (,2]\boxed{\text{Domain }[-1,\infty),\;\text{Range }(-\infty,2]}

(v) y=2x+13y=\sqrt[3]{2x+1}

Cube root is defined for all real numbers.

Pick 2x+1=8,1,0,1,82x+1=-8,-1,0,1,8.

2x+181018x92112072y=2x+1321012\begin{array}{c|ccccc} 2x+1 & -8 & -1 & 0 & 1 & 8\\ \hline x & -\frac{9}{2} & -1 & -\frac{1}{2} & 0 & \frac{7}{2}\\ \hline y=\sqrt[3]{2x+1} & -2 & -1 & 0 & 1 & 2 \end{array} Domain R,  Range R\boxed{\text{Domain }\mathbb{R},\;\text{Range }\mathbb{R}}

(vi) y=2x33y=2\sqrt[3]{x}-3

Pick x=8,1,0,1,8x=-8,-1,0,1,8.

x81018x321012y=2x3375311\begin{array}{c|ccccc} x & -8 & -1 & 0 & 1 & 8\\ \hline \sqrt[3]{x} & -2 & -1 & 0 & 1 & 2\\ \hline y=2\sqrt[3]{x}-3 & -7 & -5 & -3 & -1 & 1 \end{array}

Stretch by 2 and shift down by 3.

Domain R,  Range R\boxed{\text{Domain }\mathbb{R},\;\text{Range }\mathbb{R}}

(vii) y=x2+x23y=\sqrt[3]{x^2+x-2}

Cube root is defined for all real numbers, so domain is all real numbers.

Compute a few points:

x21012x2+x202204y=x2+x2302323043\begin{array}{c|ccccc} x & -2 & -1 & 0 & 1 & 2\\ \hline x^2+x-2 & 0 & -2 & -2 & 0 & 4\\ \hline y=\sqrt[3]{x^2+x-2} & 0 & -\sqrt[3]{2} & -\sqrt[3]{2} & 0 & \sqrt[3]{4} \end{array} Domain R\boxed{\text{Domain }\mathbb{R}}