Question 730867: Solve the following inequality. Write yur solution in interval notation.
x^3+81x>0
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Solve the following inequality. Write your solution in interval notation.
x^3+81x>0
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Factor:
x(x+9)(x-9) > 0
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Draw a number line; plot x = -9, x = 0, x = 9
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Test a value in each number line interval.
Test x = -10 to get: -*-*- > 0; false
Test x = -5 to get:: -*+*- > 0: true
Test x = 5 to get::: +*+*- > 0: false
Test x = 10 to get:: +*+*+ > 0: true
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Solution: (-9,0)U(9,+oo)
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Cheers,
Stan H.
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