Practice Problems

Answers

  1. First, we note that ‍x=1 and x=3 make at least one of the denominators zero and so neither of them is a solution.

    Now, we multiply both sides of the equation by the least common multiple of the denominators, which is (x-1)(x-3).

    \begin{aligned}\dfrac{x}{x-1}&=-\dfrac{2}{x-3}\\\\(x-1)(x-3)\cdot\dfrac{x}{x-1}&=(x-1)(x-3)\cdot\left(-\dfrac{2}{x-3}\right)\\\\x^2-3x&=-2x+2\\\\x^2-x-2&=0\\\\(x+1)(x-2)&=0\end{aligned}

    We get that x=-1 and x=2 are potential solutions. Neither of them makes the denominator zero, so they are both solutions.

    In conclusion, the solutions are x=-1 and ‍x=2.


  2. First, we note that ‍x=3 and x=4 make at least one of the denominators zero and so neither of them is a solution.

    Now, we multiply both sides of the equation by the least common multiple of the denominators, which is (x-3)(x-4).

    \begin{aligned}\dfrac{17-3x}{(x-3)(x-4)}&=\dfrac{x+1}{x-4}\\\\(x-3)(x-4)\cdot\dfrac{17-3x}{(x-3)(x-4)}&=(x-3)(x-4)\cdot\dfrac{x+1}{x-4}\\\\17-3x&=(x-3)(x+1)\\\\17-3x&=x^2-2x-3\\\\0&=x^2+x-20\\\\0&=(x+5)(x-4)\end{aligned}

    We get that x=-5 and x=4 are potential solutions. Recall that x=4 cannot be a solution.

    Therefore, the only solution is x=-5.

    x=4 is an extraneous solution, because we got it as a potential solution although it isn't actually a solution.


  3. First, we note that ‍x=3 and x=6 make at least one of the denominators zero and so neither of them is a solution.

    Now, we multiply both sides of the equation by the least common multiple of the denominators, which is (x-3)(x-6).

    \begin{aligned}-\dfrac{2}{x-3}&=\dfrac{x}{x-6}\\\\(x-3)(x-6)\cdot\left(-\dfrac{2}{x-3}\right)&=(x-3)(x-6)\cdot\dfrac{x}{x-6}\\\\-2x+12&=x^2-3x\\\\0&=x^2-x-12\\\\0&=(x+3)(x-4)\end{aligned}

    We get that x=-3 and x=4 are potential solutions. Neither of them makes the denominator zero, so they are both solutions.

    In conclusion, the solutions are x=-3 and x=4.


  4. First, we note that ‍x=-2 and x=0 make at least one of the denominators zero and so neither of them is a solution.

    Now, we multiply both sides of the equation by the least common multiple of the denominators, which is x(x+2).

    \begin{aligned}-\dfrac{2}{x(x+2)}&=\dfrac{x+3}{x+2}\\\\x(x+2)\cdot\left(-\dfrac{2}{x(x+2)}\right)&=x(x+2)\cdot\dfrac{x+3}{x+2}\\\\-2&=x^2+3x\\\\0&=x^2+3x+2\\\\0&=(x+1)(x+2)\end{aligned}

    We get that ‍x=-2 and x=-1 are potential solutions. Recall that x=-2 cannot be a solution.

    Therefore, the only solution is x=-1.

    x=-2 is an extraneous solution, because we got it as a potential solution although it isn't actually a solution.