If the -8 is under the square root, then...

OR
If the -8 is not under the square root, then...

Either way, we replace x with -3 and simplify.
For more information, refer to the direct substitution rule for limits.
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Define the numbers
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Let the first even number be x
1st even number = x
2nd even number = x + 2
3rd even number = x + 4
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Form the equation and solve
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x + x + 2 + x + 4 = -6
3x + 6 = -6
3x = - 12
x = -4
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Find the numbers
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1st even number = x = -4
2nd even number = x + 2 = -4 + 2 = -2
3rd even number = x + 4 = -4 + 4 = 0
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Answers: The numbers are -4, -2 and 0
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The Discriminant for the equation x2 + 3x - 4 = 0 would be 25.