Let \( f(x)=\frac{3 x+4}{2 x-5} \), for \( x \neq \frac{5}{2} \). (a) For the graph of \( y=f(x) \), find the coordinates of: (i) the \( x \)-intercept; (ii) the \( y \)-intercept. (b) For the graph of \( y=f(x) \), find the equation of: (i) the horizontal asymptote; (ii) the vertical asymptote. (c) Hence sketch the graph of \( y=f(x) \). (d) Find \( f^{-1}(x) \).
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The Deep Dive
Let's go through the parts of the problem step by step! ### (a) Intercepts of the graph \( y = f(x) \) (i) **Finding the \( x \)-intercept:** To find the \( x \)-intercept, we set \( f(x) = 0 \): \[ \frac{3x + 4}{2x - 5} = 0 \] This means the numerator must equal zero: \[ 3x + 4 = 0 \Rightarrow 3x = -4 \Rightarrow x = -\frac{4}{3} \] Thus, the coordinates of the \( x \)-intercept are \(\left(-\frac{4}{3}, 0\right)\). (ii) **Finding the \( y \)-intercept:** To find the \( y \)-intercept, we evaluate \( f(0) \): \[ f(0) = \frac{3(0) + 4}{2(0) - 5} = \frac{4}{-5} = -\frac{4}{5} \] Thus, the coordinates of the \( y \)-intercept are \(\left(0, -\frac{4}{5}\right)\). ### (b) Asymptotes of the graph \( y = f(x) \) (i) **Finding the horizontal asymptote:** The horizontal asymptote can be found by looking at the degrees of the polynomials in the numerator and denominator. As \( x \to \infty \): \[ f(x) \to \frac{3}{2} \] So, the equation of the horizontal asymptote is \( y = \frac{3}{2} \). (ii) **Finding the vertical asymptote:** The vertical asymptote occurs where the denominator equals zero: \[ 2x - 5 = 0 \Rightarrow 2x = 5 \Rightarrow x = \frac{5}{2} \] Thus, the equation of the vertical asymptote is \( x = \frac{5}{2} \). ### (c) Sketching the graph of \( y = f(x) \) To sketch the graph, we start with the intercepts and asymptotes. Plot the \( x \)-intercept at \(\left(-\frac{4}{3}, 0\right)\) and the \( y \)-intercept at \(\left(0, -\frac{4}{5}\right)\). Draw the vertical line for the vertical asymptote \( x = \frac{5}{2} \) and the horizontal line for the horizontal asymptote \( y = \frac{3}{2} \). The graph will approach these asymptotes but never touch them, crossing the \( y \)-axis and \( x \)-axis at the points identified. ### (d) Finding \( f^{-1}(x) \) To find the inverse of \( f(x) = \frac{3x + 4}{2x - 5} \), we replace \( f(x) \) with \( y \): \[ y = \frac{3x + 4}{2x - 5} \] Now, interchange \( x \) and \( y \) and solve for \( y \): \[ x = \frac{3y + 4}{2y - 5} \] Multiply both sides by \( 2y - 5 \): \[ x(2y - 5) = 3y + 4 \] Expanding gives: \[ 2xy - 5x = 3y + 4 \] Rearranging yields: \[ 2xy - 3y = 5x + 4 \Rightarrow y(2x - 3) = 5x + 4 \Rightarrow y = \frac{5x + 4}{2x - 3} \] Hence, the inverse function is: \[ f^{-1}(x) = \frac{5x + 4}{2x - 3} \]