Find the domain and range of the function k(x) = (x+1) / sqrt(2x+1)

Mathematics
Find the domain and range of the function k(x) = (x+1) / sqrt(2x+1)

ScanSolve AI Answer

Step 1: Find the domain

The function is defined when the expression inside the square root is positive and the denominator is not zero:

2x+1>02x + 1 > 0

Solve the inequality:

2x>12x > -1 x>12x > -\frac{1}{2}

Domain: (12,)\left( -\frac{1}{2}, \infty \right)

Step 2: Find the range

Let y=k(x)=x+12x+1y = k(x) = \frac{x+1}{\sqrt{2x+1}}.

Substitute t=2x+1t = \sqrt{2x+1} where t>0t > 0:

2x+1=t22x + 1 = t^2 x=t212x = \frac{t^2 - 1}{2}

Substitute into yy:

y=t212+1t=t21+22t=t2+12t=t2+12ty = \frac{\frac{t^2 - 1}{2} + 1}{t} = \frac{\frac{t^2 - 1 + 2}{2}}{t} = \frac{\frac{t^2 + 1}{2}}{t} = \frac{t^2 + 1}{2t} y=t2+12t,t>0y = \frac{t}{2} + \frac{1}{2t}, \quad t > 0

To find the range, analyze f(t)=t2+12tf(t) = \frac{t}{2} + \frac{1}{2t} for t>0t > 0.

Find the minimum using calculus or AM-GM inequality:

By AM-GM:

t2+12t2t212t=214=1\frac{t}{2} + \frac{1}{2t} \geq 2\sqrt{\frac{t}{2} \cdot \frac{1}{2t}} = 2\sqrt{\frac{1}{4}} = 1

Equality when t2=12t\frac{t}{2} = \frac{1}{2t}, so t2=1t^2 = 1, t=1t = 1 (since t>0t > 0).

At t=1t = 1, y=1y = 1.

As t0+t \to 0^+, yy \to \infty.

As tt \to \infty, yy \to \infty.

Thus, y1y \geq 1.

Range: [1,)[1, \infty)

Final answer

\begin{array{c} Domain: \left( -\dfrac{1}{2},\ \infty \right) \\[2em] Range: [1,\ \infty) \end{array} }
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