To solve the quadratic equation \( 84x^2 + 16x = 0 \) by factoring out the greatest common factor (GCF), we first identify the GCF of the terms.
The GCF of \( 84x^2 \) and \( 16x \) is \( 4x \). We can factor this out:
\[ 84x^2 + 16x = 4x(21x + 4) = 0 \]
Now, we can set each factor equal to zero to find the solutions:
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\( 4x = 0 \) \[ x = 0 \]
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\( 21x + 4 = 0 \) \[ 21x = -4 \] \[ x = -\frac{4}{21} \]
So the solutions to the equation are: \[ x = 0 \quad \text{and} \quad x = -\frac{4}{21} \]
From the given response options, the correct choice is: "The solutions are \( x = 0 \) and \( x = -\frac{4}{21} \)."