Solve the equation log(2x2−10)=log(x2−3x)

.(1 point)
Responses

x=−5 and x=2
x=−5 and x=2

x=2
x is equal to 2

x=−5
x is equal to negative 5

x=5 and x=−2
x=5 and x=−2

1 answer

To solve the equation \( \log(2x^2 - 10) = \log(x^2 - 3x) \), we can use the property of logarithms that states if \( \log(a) = \log(b) \), then \( a = b \) (as long as \( a > 0 \) and \( b > 0 \)).

So we will set the arguments equal to each other:

\[ 2x^2 - 10 = x^2 - 3x \]

Now, let's rearrange the equation:

\[ 2x^2 - x^2 + 3x - 10 = 0 \]

This simplifies to:

\[ x^2 + 3x - 10 = 0 \]

Next, we can factor the quadratic equation:

\[ (x + 5)(x - 2) = 0 \]

Setting each factor to zero gives us the solutions:

\[ x + 5 = 0 \quad \Rightarrow \quad x = -5 \]

\[ x - 2 = 0 \quad \Rightarrow \quad x = 2 \]

So, the potential solutions are \( x = -5 \) and \( x = 2 \).

Now we need to check if these solutions are valid by substituting them back into the original logarithmic expression to ensure that we do not take the log of a non-positive number.

  1. For \( x = 2 \): \[ 2x^2 - 10 = 2(2^2) - 10 = 8 - 10 = -2 \quad \text{(not valid)} \]

    \[ x^2 - 3x = 2^2 - 3(2) = 4 - 6 = -2 \quad \text{(not valid)} \]

    So, \( x = 2 \) is not a valid solution.

  2. For \( x = -5 \): \[ 2x^2 - 10 = 2(-5)^2 - 10 = 50 - 10 = 40 \quad \text{(valid)} \]

    \[ x^2 - 3x = (-5)^2 - 3(-5) = 25 + 15 = 40 \quad \text{(valid)} \]

Since \( x = -5 \) is valid while \( x = 2 \) is not valid, the only solution is:

\[ \boxed{-5} \]

The correct response is: x is equal to negative 5.