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Given f(x) = (3x − 2)/(5x + 4) and g(x) = (7x + 2)/(4x - 3), find (a) f⁻¹(x), (b) g⁻¹(x), and (c) the values of x if g⁻¹(x) = 1 − f⁻¹(x).

Mathematics

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3 steps
  1. Find f−1(x)f^{-1}(x) (Part a).

    Let y=f(x)y = f(x), so y=3x−25x+4y = \frac{3x - 2}{5x + 4}.
    To find the inverse function, swap xx and yy:

    x=3y−25y+4x = \frac{3y - 2}{5y + 4}

    Multiply both sides by (5y+4)(5y + 4):

    x(5y+4)=3y−2x(5y + 4) = 3y - 2 5xy+4x=3y−25xy + 4x = 3y - 2

    Rearrange the terms to isolate yy:

    5xy−3y=−2−4x5xy - 3y = -2 - 4x

    Factor out yy:

    y(5x−3)=−2−4xy(5x - 3) = -2 - 4x

    Solve for yy:

    y=−2−4x5x−3y = \frac{-2 - 4x}{5x - 3}

    This can be written as:

    f−1(x)=4x+23−5xf^{-1}(x) = \boxed{\mathbf{\frac{4x + 2}{3 - 5x}}}
  2. Find g−1(x)g^{-1}(x) (Part b).

    Let y=g(x)y = g(x), so y=7x+24x−3y = \frac{7x + 2}{4x - 3}.
    To find the inverse function, swap xx and yy:

    x=7y+24y−3x = \frac{7y + 2}{4y - 3}

    Multiply both sides by (4y−3)(4y - 3):

    x(4y−3)=7y+2x(4y - 3) = 7y + 2 4xy−3x=7y+24xy - 3x = 7y + 2

    Rearrange the terms to isolate yy:

    4xy−7y=2+3x4xy - 7y = 2 + 3x

    Factor out yy:

    y(4x−7)=2+3xy(4x - 7) = 2 + 3x

    Solve for yy:

    y=2+3x4x−7y = \frac{2 + 3x}{4x - 7}

    So,

    g−1(x)=3x+24x−7g^{-1}(x) = \boxed{\mathbf{\frac{3x + 2}{4x - 7}}}
  3. Find the values of xx if g−1(x)=1−f−1(x)g^{-1}(x) = 1 - f^{-1}(x) (Part c).

    Substitute the expressions for f−1(x)f^{-1}(x) and g−1(x)g^{-1}(x) into the equation:

    3x+24x−7=1−4x+23−5x\frac{3x + 2}{4x - 7} = 1 - \frac{4x + 2}{3 - 5x}

    First, simplify the right side:

    1−4x+23−5x=3−5x3−5x−4x+23−5x=(3−5x)−(4x+2)3−5x=3−5x−4x−23−5x=1−9x3−5x1 - \frac{4x + 2}{3 - 5x} = \frac{3 - 5x}{3 - 5x} - \frac{4x + 2}{3 - 5x} = \frac{(3 - 5x) - (4x + 2)}{3 - 5x} = \frac{3 - 5x - 4x - 2}{3 - 5x} = \frac{1 - 9x}{3 - 5x}

    Now the equation is:

    3x+24x−7=1−9x3−5x\frac{3x + 2}{4x - 7} = \frac{1 - 9x}{3 - 5x}

    Cross-multiply:

    (3x+2)(3−5x)=(1−9x)(4x−7)(3x + 2)(3 - 5x) = (1 - 9x)(4x - 7)

    Expand both sides:

    9x−15x2+6−10x=4x−7−36x2+63x9x - 15x^2 + 6 - 10x = 4x - 7 - 36x^2 + 63x −15x2−x+6=−36x2+67x−7-15x^2 - x + 6 = -36x^2 + 67x - 7

    Move all terms to one side to form a quadratic equation:

    −15x2+36x2−x−67x+6+7=0-15x^2 + 36x^2 - x - 67x + 6 + 7 = 0 21x2−68x+13=021x^2 - 68x + 13 = 0

    Use the quadratic formula x=−b±b2−4ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} with a=21a=21, b=−68b=-68, c=13c=13:

    x=−(−68)±(−68)2−4(21)(13)2(21)x = \frac{-(-68) \pm \sqrt{(-68)^2 - 4(21)(13)}}{2(21)} x=68±4624−109242x = \frac{68 \pm \sqrt{4624 - 1092}}{42} x=68±353242x = \frac{68 \pm \sqrt{3532}}{42}

    Calculate the square root:

    3532≈59.43063\sqrt{3532} \approx 59.43063

    Now find the two values for xx:

    x1=68+59.4306342=127.4306342≈3.03406x_1 = \frac{68 + 59.43063}{42} = \frac{127.43063}{42} \approx 3.03406 x2=68−59.4306342=8.5693742≈0.20398x_2 = \frac{68 - 59.43063}{42} = \frac{8.56937}{42} \approx 0.20398

    Rounding to two decimal places:

    x1≈3.03x_1 \approx 3.03 x2≈0.20x_2 \approx 0.20

    The values of xx are 3.03 and 0.20\boxed{\mathbf{3.03 \text{ and } 0.20}}.

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